Australia's Jason Day, chasing his first US PGA victory since 2018, fired an eight-under par 62 despite a sore back to seize a one-stroke lead Friday at the Travelers Championship.
The former world number one, who last won three years ago at Quail Hollow, fired eight birdies in a bogey-free round to stand on 131 after 36 holes at TPC River Highlands in Cromwell, Connecticut.
Day was one stroke ahead of two-time Masters champion Bubba Watson and first-round co-leader Kramer Hickok with England's Justin Rose and South Korean Lee Kyoung-hoon in a pack on 133.
"Body is OK. Just stiff," Day said. "Any time going left was a little bit sore. I haven't had time to really rest it since I kind of put it out."
Day, the 2015 PGA Championship winner, missed three consecutive cuts before sharing 44th at the PGA Championship then withdrew from the Memorial with a back injury earlier this month.
"Having a couple weeks off was great, but you just need a little bit more time is what it is," Day said.
Back-nine starter Day birdied the par-3 11th and par-5 13th from inside five feet and holed a 12-foot birdie putt at the 18th to start a run of three in a row.
Day dropped his approach inches from the cup at the fourth for a tap-in birdie then rolled in a 36-foot birdie putt at the par-3 fifth and added another from 14 feet at the seventh before sinking a 10-foot par save putt at the eighth.
"Sometimes when you do have sort of an injury or stiffness, even if you're sick, sometimes you can come out and play some good golf," Day said.
"I was fortunate enough to not really get in my own way today. Hit a lot of good quality drives and my tee to green was pretty solid, I thought. Then holed a lot of crucial putts out there so that's what kept everything rolling."
Watson shot 66 despite snapping his pink driver, which snapped apart during his swing on the second tee.
"My driver head popped off," Watson said. "It's the shaft right above the hosel. It's cracked, broke, whatever you want to call it.
"I always have a back up. They brought me the back up two holes later and I played with that the rest of the day."
Watson, who won green jackets at Augusta National in 2012 and 2014, began on the back nine and sank a 10-foot birdie putt at the par-5 13th hole and another at the par-4 second.
Watson then charged with three birdies in a row, making putts inside five feet at the par-3 fifth and par-5 sixth before rolling in a 50-foot birdie putt at the seventh, but missed a three-foot par putt at the ninth for his lone bogey.
"Didn't read it right," Watson said. "Even though it was short, it still has movement enough to miss the hole like it did."
Watson's 12 US PGA titles include three wins at the Travelers, including his first tour title in 2010, another in 2015 and his most recent US PGA victory in 2018. The first two came in playoffs.