Early career

In partnership with Thayne Green and Helen Lusty, McKee raced Sunline as a two-year-old. She was unbeaten in three starts.

After a first-up win at three, in August 1998, the McKees took Sunline to Australia for the first of an eventual nine visits. Racing in the second, third, and fourth legs of Sydney's Princess Series, for three-year-old fillies, she powered through the slop on her Australian debut in the Furious Stakes,^[5] won the Tea Rose Stakes^[6] on a dry track two weeks later, and then took the Flight Stakes^[7] - her first of 13 Group One wins. Sunline was then spelled, rather than continuing on to the feature races in Melbourne, and never competed with the reigning Horse of the Year, Might And Power.

Sunline resumed in February 1999. She won first up but was narrowly beaten for the first time by Rose O'War, second-up, in Melbourne's Angus Armanasco Stakes, her 9th career start. The race was not run to suit, with a long shot racing away before the home turn, which may have exposed Sunline's lack of fitness on the day, as she was jumping from 1,200 to 1,600 metres. At her next start, Sunline defeated Rose O'War in the Kewney Stakes, and in her first look at the Cox Plate course, defeated the VRC Oaks (and subsequent AJC Oaks) winner Grand Archway by 4+1⁄2 lengths in the Moonee Valley Oaks (2,040 metres).

Sunline then ventured north to Sydney to tackle the Doncaster Handicap (1,600 metres).^[8] Despite taking on older horses for the first time, and starting from a wide starting gate, Sunline was sent out one of the shortest-priced favourites in the race's long history,^[9] at 10/9 (approximately $2.10). Sunline went straight to the front and never looked back to score by one-and-three-quarter lengths. She became just the fourth filly to win in the modern history of the race.

A fortnight later, Sunline was again a favourite in the Queen Elizabeth Stakes (2,000 metres), and led the field over the rise (near the top of the straight), then faded to finished second-last of the six runners. She was then sent home to New Zealand for a spell.

1999/2000: Four-Year-Old Season

Unlike many three-year-old champions, Sunline made the transition to weight-for-age racing as four-year-old. First up, she scored a win over the multiple Group One winner Tie the Knot in the Warwick Stakes and was installed ante-post favourite for the $3 million W. S. Cox Plate at Moonee Valley. At her next two starts, Stephen and Trevor McKee then tried to get the mare settle in her races, but she was narrowly defeated in the Theo Marks Quality (by Adam) and the George Main Stakes (by Shogun Lodge). Her final lead-up to the Cox Plate was a close fourth under 56.5 kilograms (8 st 11 lb) in the Epsom Handicap.

Speculation in the media^[10] that Sunline would be vulnerable in the Cox Plate - in open company over 2,040 metres - proved unfounded. Leading before the home turn, Sunline held off a late challenge from Tie the Knot, with Caulfield Cup winner Sky Heights in third place. Sunline became only the fifth mare to win the race since its inception in 1922 and the second of four mares to win the race since Dane Ripper in 1997 (the others being Makybe Diva in 2005 and Pinker Pinker in 2011).

After a brief let-up, Sunline came back in distance and defeated other mares in the Auckland Breeders' Stakes (1,400 metres), in New Zealand, in preparation for the International Cup (2,000 metres) in Hong Kong. Sunline led, and her jockey, Greg Childs, explained that she travelled well to the home turn, but, in an echo of the autumn's Queen Elizabeth Stakes, tired badly in the home straight and finished seventh. She then returned home to New Zealand for a spell.

Back in Sydney for the autumn of 2000, Sunline powered through the rain-affected going to win the Apollo Stakes (1,400 metres) first-up. In her entire career, she was never beaten over the distance. She then carried the maximum topweight (60 kilograms) to win the first of two Coolmore Classics - at the time, Australia's only Group One race for fillies and mares (three years and over). At her next start, she carried 57.5 kilograms (9 st. 1 lb.) in the Doncaster Handicap and was narrowly defeated by the lightly weighted three-year-old Over. Meeting again a week later, in the All-Aged Stakes, Sunline relished the return to weight for age conditions - accounting for Georgie Boy, with Over in third place, to make it three wins from four starts this campaign.

2000/2001: Five-Year-Old Season

Sunline started her five-year-old campaign in Melbourne, against the sprinters - streaking away in the Manikato Stakes (1,200 metres) at Moonee Valley. She then had wins in the Memsie (1,400 metres) and Feehan Stakes (1,600 metres), but was narrowly beaten by Fairway in the Turnbull Stakes (2,000 metres). A natural frontrunner, like Sunline, Fairway refused to hand up the lead to Sunline, who was forced to chase, and held her at bay down the straight. It was Sunline's third defeat over the distance from as many starts away from Moonee Valley, but it was a great improvement on her previous defeats, especially since Fairway was a multiple Group One winning three-year-old the previous season.

Sunline fans regard her next run as one of her greatest.^[11] On the last Saturday of October, Sunline took control in the rain-affected going to win the Cox Plate by seven lengths from Caulfield Cup winner Diatribe, with Referral in third place.^[12] Perhaps unsuited in the conditions, fancied runners Tie the Knot (2nd in 1999), Sky Heights (3rd in 1999), and Shogun Lodge (conqueror of Sunline in the George Main Stakes) were beaten a combined margin of more than 100 lengths. In winning, Sunline became the first Australasian horse to pass $6 million in career earnings.^[13]

International Success

Returning to New Zealand after the Cox Plate, the mare's owners revealed that Sunline had been part of a bidding war from five different countries, including the powerful Godolphin stables in the United Arab Emirates. All bids were rejected, and the mare was prepared for another trip to the rich, pre-Christmas international meeting in Hong Kong. In her final lead-up, Sunline raced away with the Auckland Breeders' Stakes at Pukekohe. In Hong Kong, she led all the way to win the International Mile (1,600 metres),^[14] narrowly holding off local icon Fairy King Prawn, with five lengths back to Adam in third place.

While the victory in Hong Kong neither confirmed nor denied the oft-made claim of her fans that Sunline was world's best racemare, her Cox Plate victory saw the Australian and New Zealand Horse of the Year receive an invitation to compete in the world's richest raceday, the Dubai World Cup meeting in the United Arab Emirates.

In early February, Sunline recorded her eighth win in New Zealand when she was too good for seven other Group One winners in the Waikato Sprint. The victory kept alive Sunline's wonderful record in her home country, which at career end would stand at 11 wins from as many starts. Sunline's next step came with a hit-and-run trip to Sydney for the Apollo Stakes at Warwick Farm. For the second year in a row, the race was run on a rain-affected track, and Sunline accounted for Celestial Choir, with Tie the Knot unplaced.

In Dubai, Sunline showed her customary pace to lead the field in the Duty Free (1,800 metres), but her breakaway tactics were not aided by a home straight of 600 metres. Jim And Tonic and Fairy King Prawn loomed up to Sunline with 200 metres to run, and after a tough run, Sunline did well to hold on for third.

She returned to Australia to contest the All Aged Stakes against a sub-standard field on a wet track at Randwick. Starting a hot favourite, Sunline was narrowly defeated by El Mirada and Final Fantasy, and then given time off from racing.

2001/2002: Six-Year-Old Season

The six year old Sunline returned with a close second to Piavonic in the Manikato Stakes. She then won the Memsie Stakes for the second year in a row, but was defeated by Northerly in the Feehan Stakes. She rebounded to win the Turnbull Stakes in her fourth start of the season.

Sunline was defeated by Northerly again in the Cox Plate, where a third victory would have equalled the record set by Kingston Town. Just like in the Feehan Stakes, In both races, Sunline led to the home turn, but Northerly surged to the front in the straight. The race featured three controversial protests: Sunline (second) against first (Northerly), and third (Viscount) against first and second. The protests arose from heavy contact between the three horses in the straight, with Northerly on the outside, Sunline closest to the rails, and Viscount in between. All three protests were eventually dismissed on twin grounds that stewards were unable to determine which riders were at fault or satisfy themselves that the interference had affected the result.^[15]

Following her spring defeats by Northerly, she returned in the autumn of 2002 to race four times for as many wins - all in Group One races. Each of her nine starts for the season came in races she had also contested in the last two seasons, and returned six wins from nine starts (a winning strike-rate of 67%), compared to eight from 11 in the 2000–2001 season (73%), and six from 11 in the 1999–2000 season (55%).

The first of these was a win by four lengths in Waikato Sprint at Te Rapa (defeating Ethereal, who was out-paced in her first run since the Melbourne Cup).^[16] She then won the Coolmore Classic for a second time - again carrying the race's maximum handicap of 60 kilograms - and became the first horse in Australasia to win A$9 million in prize money.^[17]

At her next start, she carried the number one saddlecloth to victory in Doncaster Handicap. With 58 kilos, she defeated Shogun Lodge (who also carried 58 kilos) and Defier (who carried 51.5 kilos but was trapped wide). She closed her campaign with a six length victory in the weight-for age All-Aged Stakes. By winning these races, she became the first horse in Australasia to pass the $11 million mark in career earnings and with 13 Group One wins, she was within one of Kingston Town's record of 14 Group One races.

In the next spring, Sunline notched her fifth consecutive win when taking the Mudgway Stakes first-up in New Zealand, and returned to Sydney for the George Main Stakes. Sunline led but was run down by Defier and Excellerator. In her next start in the Caulfield Guineas Sunline led, and, to a huge roar from the crowd, skipped away by more than three lengths at the top of the straight, but Lonhro loomed up strongly close to home to score in race record time, with a margin of six lengths back to the third horse.^[18]

The clash may have flattened Sunline and Lonhro, who appeared to race below their best when fourth and sixth,^[19] respectively, behind Northerly in the Cox Plate. As planned, Sunline was retired after this, her fourth and final Cox Plate, and her record of two wins, a second, and a fourth is one of the best in the history of the race.