Rory McIlroy, Lee Westwood and David Lynn are all battling to win the Wells Fargo Championship - as tournament officials battled the weather in North Carolina.
Tee times in the final round were brought forward by several hours and the players sent out in threeballs from the first and 10th tees in an attempt to avoid the heavy rain which was forecast.
McIlroy, who celebrated his 24th birthday on Saturday, got off to a poor start with a bogey on the first, but hit back with birdies from 12 feet on the third and fourth.
Another birdie on the par-five seventh took the world number two to the turn in 34 and into a share of second place with Lynn and Westwood on seven under par.
Lynn, second behind McIlroy in the US PGA Championship at Kiawah Island last year, had also dropped a shot at the first but picked up shots on the seventh and eighth, while playing partner Westwood had birdied the first from 15ft.
The former world number one dropped a shot on the third after missing the green with his approach and hitting a poor chip, but bounced back with a birdie on the fifth to trail Mickelson by one shot.
Mickelson had matched Westwood's bogey at the third but also matched his birdie at the fifth, while Watney had carded six pars and one bogey in his first seven holes.
At seven under he shared second place with McIlroy, Lynn, Westwood and Sweden's Robert Karlsson.