Short-priced favourites in the two feature races ensure Joao Moreira is top pick in Sunday's Jockey Challenge at Sha Tin, but better value may be found shopping elsewhere - and backing Zac Purton - on an otherwise wide-open day.

Sterling City was early favourite in the Group One Chairman's Sprint Prize and looks a safe bet to score points for Moreira from a Jockey Challenge perspective and Able Friend is a bombproof four-year-old coming off a dominant win in the Group One Hong Kong Classic Mile, and could start odds-on in the Group One Hong Kong Classic Cup.

Purton lacks the top-end firepower of the favourite, but starts the day more strongly than he finishes it, and some specking on him at $6 - avoiding the early $2.25 on offer about Moreira - could pay off. Purton actually has the numbers advantage over the Brazilian - nine rides to eight - and his first four rides, in the first four races, look better than his rival's in the corresponding contests.

The rest of the day is peppered with outsiders for Purton, but Peter Ho Leung-trained Archippus looks a great bet in race.

If Purton or any of Moreira's other rivals can't pinch a substantial break at the halfway mark of the meeting, he should be able to gun them down with his back-ended day finishing with a string of top chances. The trouble with betting against Moreira in the Jockey Challenge of late is that he still somehow manages to win when having a "bad" day, or when someone else has a massive day - like last Saturday when Tye Angland rode a treble but was still beaten by the Magic Man.