Webb Simpson fired nine birdies in fashioning a six-under par 65 on Friday for a one-stroke lead midway through the PGA Tour RBC Heritage.

Simpson said distance control was the key to his second straight six-under effort at Harbour Town Golf Links in Hilton Head Island, South Carolina, where his 12-under total of 130 put him one clear of American Bryson DeChambeau and Canadian Corey Conners.

Simpson and DeChambeau were a study in contrasts playing in the same group.

DeChambeau is cutting an impressive figure after using the coronavirus hiatus to add about 20 pounds (9kg) in a quest for more strength and speed that he launched late last year.

He said the narrow Harbour Town layout didn't allow him to make the most of his newfound power, but he still grabbed eight birdies in a seven-under par 64 for 131.

"It's just this golf course, it's so difficult to try to fit into these tight areas where, if you miss it offline, like I did last week a couple times on a couple holes, I'll be blocked out," DeChambeau said.

Six of DeChambeau's birdies came in his last nine holes, but he missed a five-foot birdie putt at his final hole, the ninth, where Simpson rolled in a six-footer to cap a birdie-birdie finish.

"It's very satisfying knowing I'm not near as long as some of these guys and I'm able to kind of use my skills of distance control and shot shape to pick me back up when I'm 40 yards or 30 yards behind these guys," said Simpson, the 2012 US Open champion.

"I would like to hit it further," added Simpson, who has taken a long, methodical approach to gaining strength and distance without compromising any aspect of his game.

"I set out on a journey three years ago to get stronger, hit it further, but do it a lot slower than Bryson," he noted. "But he's made it look easy and seamless."

Conners joined DeChambeau on 131 after a "stress-free" 63 that featured eight birdies without a bogey.

It was a further stroke back to American Ryan Palmer, who posted a 67, and England's Matthew Fitzpatrick signed for a 66.

Former world No 1 Brooks Koepka carded a 66 to head a group on 133 that also included overnight co-leader Ian Poulter of England (69), Venezuela's Jhonattan Vegas (63), Mexico's Abraham Ancer (64) and American Matthew NeSmith (67).

First Covid-19 positive case

World No 1 Rory McIlroy rallied after a disappointing first-round 72 with a bogey-free 65 that saw him make the cut with a stroke to spare.

The tournament is the second since the PGA Tour resumed after a three-month break caused by the coronavirus pandemic.

Officials announced that US veteran Nick Watney had withdrawn from the tournament on Friday after becoming the first player since competition resumed to test positive for COVID-19.

The tour said in a statement that Watney was re-tested on Friday after complaining of symptoms and had gone into self-isolation.

"For the health and well-being of all associated with the tournament and those within the community, the tour has begun implementing its response plan in consultation with medical experts, including working with those who may have had close contact with Nick," the tour said in a statement.

Leading second-round scores on Friday in the PGA Tour RBC Heritage at Harbour Town Golf Links in Hilton Head Island, South Carolina (USA unless noted, par-71):

130 - Webb Simpson 65-65

131 - Bryson DeChambeau 67-64, Corey Conners (CAN) 68-63

132 - Ryan Palmer 65-67, Matthew Fitzpatrick (ENG) 66-66

133 - Abraham Ancer (MEX) 69-64, Jhonattan Vegas (VEN) 70-63, Matthew NeSmith 66-67, Brooks Koepka 67-66, Ian Poulter (ENG) 64-69

134 - Mackenzie Hughes (CAN) 66-68, Dustin Johnson 68-66, Dylan Frittelli (RSA) 65-69, Tyler Duncan 71-63, Sam Ryder 69-65, Wyndham Clark 68-66, Sebastian Munoz (COL) 65-69, Tony Finau 66-68, Ernie Els (RSA) 67-67, Michael Thompson 65-69, Erik van Rooyen (RSA) 66-68

135 - Danny Lee (NZL) 68-67, Andrew Landry 68-67, Jason Dufner 69-66, Alex Noren (SWE) 69-66, Sergio Garcia (ESP) 70-65, Tyrrell Hatton 71-64