Ben Martin shot a prolific third-round 62 to take a two-shot lead into the final day at the Shriners Hospitals for Children Open in Las Vegas.
The American sank no fewer than 10 birdies on day three at TPC Summerlin to finish his round on 17-under par, two strokes clear of Scotland's Russell Knox.
Knox, who went into the Saturday session as co-leader on 10-under, carded a bogey-free 66 to remain in contention ahead of the final day in Vegas.
Like Martin, Jimmy Walker also came from nowhere to shoot 62 and leave himself third on 13-under.
Walker, who registered 69 on both Thursday and Friday, managed the seven-shot improvement by holing nine birdies and avoiding any blemishes on his card.
Four players head into Sunday on 12-under - Webb Simpson, Brooks Koepka, Kevin Streelman and Scott Piercy.
