Zack Sucher threw away a commanding lead in a rapid back-nine collapse on day three of the Travelers Championship, opening the door for Chez Reavie to surge ahead with a superb seven-under round.
Sucher had pulled clear of the pack on Friday to hold a two-stroke overnight lead at TPC River Highlands and the American set about building on that advantage on Saturday, making three birdies before the turn to open up a five-shot lead.
However, a bogey on the 10th was followed by doubles at 11 and 12 to unseat Sucher - chasing a maiden PGA Tour title - at the summit.
Reavie, who had been joint second heading into Saturday's action, capitalised on his compatriot's misfortune, making gains on seven of his second nine holes.
The performance, which featured eight birdies in total, took Reavie to 16 under for the tournament, six clear of closest challengers Sucher and Keegan Bradley.
Jason Day and Roberto Diaz are a shot further back, while Bryson DeChambeau - who went six under on Saturday - and leading British players Tommy Fleetwood and Martin Laird are among four men at eight under.
Reavie, now in the box seat to win his first PGA Tour title since the 2008 Canadian Open - his only victory to date - finished in a tie for third at last weekend's US Open, which represents his best finish at a major.