Lahiri, who had 68 and 74 on the first two days, once again had problems on the back nine, where he dropped three shots in the five-hole stretch between 13th and 17th.
Lahiri is now five-over 215 and in tied-30th spot, after being tied-fifth on the first day. Lahiri's two birdies in the third round came on sixth and eighth, but he dropped shots on fourth, ninth, 13th, 14th and 17th. The birdies were from 13 and 16 feet, but he also missed a few short one like the par putt from just four feet on ninth and a birdie putt from under six feet on 10th.
Day hit only three fairways on a Firestone course that demands more, but still managed a 1-under 69 to share the lead with Piercy. But he did have three par putts of at least eight feet.
Piercy, coming off a runner-up finish in the U.S. Open two weeks ago at Oakmont, quickly tied Day for the lead with an eagle on the par-5 second hole and was flawless until the final hole. He pulled his tee shot into the left rough and just managed to escape with a bogey and a 67.
David Lingmerth of Sweden had a 69 and was one shot behind. The big move Saturday belonged to U.S. Open champion Dustin Johnson, who hits it a long way and has a short memory.
Spieth had another 71 and was five shots behind the leader.