Hours after Spieth played his way back into contention with a 9-under 62, Troy Merritt birdied each of his last four holes to card a 10-under 61. The score tied a course record at Harbour Town previously set by David Frost in 1994, and at 12 under Merritt leads Matt Kuchar and John Merrick by four shots after two rounds.
"I've got a superstition that when I make a birdie, I don't take a ball out of the round," Merritt said. "I put the last ball into play on 12, and it got beat up the last seven holes but I played it all the way in and made six birdies with it."
Merritt began slowly, playing his first six holes in 1 under, but he made the turn after birdies on Nos. 7 and 9 and caught fire on his inward half. The 29-year-old carded a 7-under 28 on the back nine, and his 12-under 130 total is one shot off the previous tournament record for 36 holes.
Merritt has been one of the PGA Tour's best putters this season - he ranks fifth in strokes gained putting - but he had everything working during the second round.
"It's all about tempo for me, and the tempo was pretty solid today," he said. "There's just a few rounds where that tempo was spot-on on just about every swing, and I had that coming down the stretch."
Merritt only has one top-25 finish in 13 starts this season, a sixth-place showing at the Valspar Championship last month. He will now be the man to beat this weekend as he eyes his first victory, with his previous career-best result a runner-up at the FedEx St. Jude Classic last year.
"Obviously we're only halfway through the tournament. I've got a couple-shot lead on some very good guys, past champions," Merritt said, referencing Kuchar, Graeme McDowell and Jim Furyk, all inside the top 10. "Just enjoy the moment, have fun with them, hit some good shots, not think about it too much and just add it up at the end."