The Australian had all but written off his chances of matching his Brazilian rival's epic 170 – set in the 2016/17 season. Purton entered the campaign's third-last fixture today requiring 12 wins: his timely haul left him six behind with 20 races remaining, spanning nine at Wednesday's Happy Valley meeting and 11 at next Sunday's Sha Tin finale.
"Six winners is a huge effort, of course it is, but I still need six more just to match Joao and I don't know if I've got the horses to do that," he said.
The ace rider completed his fourth six-timer of the campaign aboard the Frankie Lor-trained Marvellous World in the Class 4 Beijing Clubhouse Handicap (1200m).
Purton's fifth win came in race seven and turned up the heat in the trainers' premiership. An astute ride on the John Moore-trained Magic Success took the handler to within one win of long-time leader and defending champion John Size.
"It's going right to the wire," Moore said after seeing his season's tally increase to 73. "On Wednesday, we're very strong, and then on the last day we have the big boys out again when Thanks Forever will be back out with Zac on board."
Size has a good hand to play on Wednesday night too when both handlers could saddle eight runners apiece.
Magic Success's win under Purton in the Class 4 Beas River Country Club Handicap (1400m) was the gelding's second from four starts since a mid-season transfer from the David Hall stable.
"That was terrific; it was a great ride from Zac," Moore said. "He thought the guy in front was going to go on and he didn't, and he didn't want to be behind him so by the 700 (metres) he was already off the fence, three deep, and he went up and put Moreira in a pocket. That was the end of it and the horse won well – with the blinkers off he wasn't racing as aggressively as he has done before."
Hall, too, was a beneficiary of Purton's hot streak, although the ease with which both Mr Genuine and Lucky Time landed their winners' cheques meant that the rider did not have to get overly strenuous in the run home.
The former nailed a two-length win in the Class 3 Racing Heritage Handicap (1200m) and the latter sauntered to a three and three quarter-length score in the Class 4 Sha Tin Clubhouse Handicap (1600m).
"It's great to get the win with Mr Genuine," Hall said of the eight-year-old. "We had a frustrating season when he put all those seconds together and he's had another frustrating season this time around with a few thirds. He's a bit long in the tooth so to get the win was great. Mr Genuine doesn't handle the good to firm tracks."
Mr Genuine started the season rated 90 but won today off 72, while the 60-rated Lucky Time was winning for the first time since he prevailed off 62 in May last year.
"I thought Lucky Time's last run was solid and with the drop in grade I expected him to run very well today," Hall continued.
"Lucky Time came with a problem and he's also not comfortable on good to firm but he's been able to work through it. He got the right sort of conditions down in class, he had Zac on and he was too good."
Hall is pleased with how the later part of the season has panned out for his yard.
"We had a dry run in the middle section of the season but we've finished off good," he said. "We had Little Giant and Ho Ho Khan both winning a Group 3 and now we're continuing on with the winners to back it up, so we're pretty satisfied that the season's gone well and we're looking forward to next season."
Purton's half dozen started in race two aboard the Paul O'Sullivan-trained Wayfoong Charmer and also featured a score on the Benno Yung-trained Cool Celeb in race five.
Unicorn sprints to Cup win
Purton had to settle for second in the afternoon's feature as Classic Unicorn (116lb) made it two from two in the afternoon's feature, the Class 3 Members Cup Handicap (1000m).
The champ had been in the plate for the three-year-old's debut but handed the reins to Derek Leung when the Chris So-trained gelding was allotted a weight below Purton's minimum. The chestnut sprinted home in 55.09s, a length and a quarter ahead of Purton on Seven Heavens (133lb).
"He's a nice horse," So said. "He showed good pace again. I think he'll better after next season and in future I think he can go 1200 and 1400 metres but not yet, he's still learning a lot. He doesn't concentrate but when the pressure comes he kicks.
"A lot of people called me in the last two days because he had lost 40 pounds from his last run but his blood tests were good, he was eating well. You can't take weight as a standard from his first run, he's a baby, so for me, I thought he'd run well."
Classic Unicorn's win sealed a double for So. The eight-year-old Lotus Breeze took race three, the Class 5 Ownership Pride Handicap (1400m), under Chad Schofield.
Size went close to regaining his two win lead over Moore when Red Desert set for home under Joao Moreira in race 10, the Class 3 Levade Handicap (1200m). But Karis Teetan had other ideas and drove hard and late to take the spoils by a short-head on Coby Oppa, delivering a Lor double in the process.
Jockey Vincent Ho and trainer Francis Lui continued their season of success together when Farhh Above took the opening Racing Club Plate (1200m) for Griffins.
Hong Kong debutant Star Performance took the last, the Class 3 Members Care @HKJC Handicap (1400m) under Dylan Mo. Tony Cruz's New Zealand import ran a couple of solid races in G2 company before his arrival at Sha Tin.
Hong Kong racing continues at Happy Valley with a nine-race card on Wednesday, 10 July.