Sunday could be the day Zac Purton clinches his sixth Hong Kong jockeys’ title, and John Size, who prepares four of the Australian rider’s good chances, takes a giant leap towards his 12th trainers’ championship.

Unless Vincent Ho Chak-yiu rides at least four more winners than Purton during Sunday’s 10-race meeting, the 40-year-old pilot will leave Sha Tin after the twilight programme to celebrate joining Hong Kong legend Tony Cruz on half a dozen jockeys’ crowns.

Central to Purton’s weekend aspirations of making it mathematically impossible for Ho to overtake him and closing in on Joao Moreira’s single-season mark of 170 victories is Size, for whom he steers Tuchel, Beauty Eternal, Golden Express and Helios Express.

Size – who holds an eight-win lead over his former assistant, reigning champion trainer Frankie Lor Fu-chuen, with 76 races left on this term’s programme – is seeking to move one title clear of George Moore.

Tuchel may not have a better opportunity to bank his first black-type winner’s cheque than the one that presents itself in Sunday’s eight-runner Group Three Premier Plate (1,800m) at handicap conditions.

None of the three Premier Plate starters burdened with heavier imposts than Tuchel is in great form, while the Classic Mile and Derby (2,000m) runner-up appears to have a class edge over his four other opponents, three of whom will carry more weight than Jockey Club handicappers think they should lug.

Tuchel cost favourite backers in a Class Two contest over 1,800m last month, but Size thought the four-year-old Redwood gelding acquitted himself with distinction in the circumstances, placing third on a soft-rated surface under 135 pounds.

“Rain-affected tracks are always a bit tricky to assess horses on, but I thought it was a sound effort,” Size said of Tuchel’s run behind stablemate Bourbonaire and All For St Paul’s.

“He finished in the money. With the weight and the conditions, maybe you could forgive him for not winning. I think he still raced very well.

“He’s done well at home, so I think he’ll run well again. On paper, the race looks suitable.”

Beauty Eternal won a Group Three event three weeks ago, and the Hong Kong Derby third will attempt to parlay his Lion Rock Trophy (1,600m) triumph into Group Three Premier Cup (1,400m) success on Sunday’s card.

Asked what he thinks is Beauty Eternal’s optimal trip, Size said his team were gathering more data before planning the galloper’s future itinerary.

“Distances are best defined when horses get up in class and run at their own level, so we haven’t narrowed it down yet. By the time Beauty Eternal comes back next season, I’m sure we’ll have a good idea what he can do,” said 68-year-old Size.

“He’s done everything we probably expected of him. He’s always shown plenty of potential and good ability, and he hasn’t disappointed us yet, so I think he’s probably going to run well again.”

Size is double-handed in the Premier Cup, with Class One Hong Kong Macau Trophy (1,400m) winner Red Lion trying to confirm course-and-distance form against Beauty Eternal, whom he beat by nearly two lengths.

Red Lion, winner of four of his past five starts, has impressed Size since he landed in Hong Kong 10 months after his Royal Ascot seventh in the Britannia Stakes (1,600m) for Andrew Slattery.

“The first day we raced him, he ran really well at Happy Valley,” Size said of Red Lion. “He came from an outside gate and showed good speed. He stuck on, so he looked like a racehorse from the outset.

“He’s developed and gone on with it. He’s been quite workmanlike, but he keeps going up in class. He’s done a lot of good things. He’s handled the wet tracks. He’s handled the firm tracks. Overall, he’s been a very good horse for us.”

Hewitson hopes to have whale of a time on projected Premier Plate leader Beluga

With Purton committed to Beauty Eternal, Alexis Badel will reunite with Red Lion after the French rider stood aside for the Australian jockey last time.

Hat-trick scorer Golden Express and Helios Express, who made a favourable impression on his local debut, are Size’s top chances outside Sunday’s Group races.