While premiership pacesetter Douglas Whyte and his arch-rival Brett Prebble take their worthy places at the top of Jockey Challenge betting today, Zac Purton looks a value chance to upset them at his overnight quote of $16. Purton has two excellent chances in topweight and last-start winner Buccaneer in the seventh event, the Class Three sprint on the all-weather, and Lambro in the final event. Lambro, prepared by Sean Woods, was a good thing beaten last time and looks well placed to make full amends. If they both win, they will give him 24 points and that might not be enough for victory. His remaining five mounts are all at double-figure odds and it may be that his best chance of getting some early runs on the board rest with the griffin, Be Grateful, in the opening event. Be Grateful, a three-year-old by Fusaichi Pegasus, went nicely on debut for fifth to Malayan Bright on March 23, and his subsequent placing in an all-weather trial suggests he has come on well for the run. Last night, Prebble headed the market at $28 with his shortest-priced mount being fallen idol Sacred Kingdom in the Sprint Cup. But he's also on strongly fancied runners Gallant Master and Osvaldo, giving him a good chance of making it back-to-back wins in the competition after cleaning his rivals out on Audemars Piguet day last Sunday.