Winning hoop Purton said he felt Aerovelocity won despite being below his best.
"It's a good feeling, because we're of the opinion we're starting to lose him," Purton said.
"We know he's a warrior and he gives everything he's got, and although he didn't perform at his best today, his heart's just so big he was able to give us that effort.
"He [O'Sullivan] had, he'd fine-tuned him and he'd dropped the extra few pounds he was carrying and got him as best as he could for today, so he's done a great job.
"We had a lovely run in the race, and we come out and he was able to amble up. It was hard-fought in the end, but as I said, he's all heart."
It has taken a suspension to halt Craig Grylls' winning streak.
The Matamata rider has had a remarkable run, winning a group race in each of the past four weekends.
However, his hopes of extending that run on Chocante in next Saturday's group three Manawatu Cup have been ended.
Grylls received a three-day suspension after the last race at Ellerslie on Sunday, with the suspension beginning after the Matamata meeting on Wednesday.
Danielle Johnson, who has already had two wins on Chocante, will now have the Manawatu Cup mount.
Grylls could have chosen to ride at Awapuni but that would have meant he missed the Boxing Day meeting at Ellerslie, which is one of the most lucrative of the season, with stakes of $740,000.
In particular, Grylls hopes to partner Coldplay in the Zabeel Classic (2000m) on Boxing Day.
He is unbeaten from two mounts on Coldplay, which have produced wins in the Eagle Technology Stakes (1600m) at Ellerslie on November 26 and last weekend's Cal Isuzu Stakes (1600m) at Te Rapa.
The Savabeel mare won comfortably at Te Rapa and Grylls expects her to cope with a middle distance.
Grylls, 26, has never been a self-promoter but is having a vintage season. He is in third place on the premiership, with 36 wins, and has won six black-type races this term, more than any other rider.
Five of his feature wins this term have been in group races. He won the group one Livamol Classic on Willie Cazals in October before winning the group three Counties Cup, Eagle Stakes, group two Wakefield Stakes and the Cal Isuzu in successive weekends.
He won seven races from December 3 to December 11, beginning with two wins, including the Wakefield, at the premier meeting at Trentham and had another double at the premier meeting at Te Rapa.
He has nine rides at Matamata tomorrow and the suspension will allow him to "freshen up" before the hectic Christmas schedule.
"Things are going well," Grylls said. "I've been getting on some classy horses and that definitely helps.
"I didn't start the season with any specific targets, apart from wanting to ride as many winners as I can, though you usually try to do better than in the previous season."
Grylls, whose career tally in New Zealand is approaching 700, is six wins behind premiership leader Danielle Johnson. "I would consider having a go [at the premiership] if I'm still in contention late in the season but I've got no plans to ride here, there and everywhere."
- additional reporting, NZ Racing Desk.
