Former US Open champion Webb Simpson delivered a putting master class to grab the second-round lead at the RBC Heritage in South Carolina.

Simpson mixed nine birdies with three bogeys for a six-under-par 65 that left him at 12-under for the week at Harbour Town course on Hilton Head Island and one shot clear of Bryson DeChambeau (64) and Canadian Corey Conners (63).

"I had a few par savers that kind of kept my momentum going, but I did drop three shots, all kind of physical errors," said world number nine Simpson.

"I'm thinking well right now, so I'd rather physical errors than mental errors."

It was a good day's work for Rory McIlroy, as he hit six birdies to sign for a round of 65, moving him to five-under-par, and guaranteeing him weekend play.

But Shane Lowry and Graeme McDowell missed out, despite both making big improvements on their first-round efforts. The pair finished on one-under, three shots outside the cut mark of four-under-par.

McDowell hit seven birdies in a five-under 66, while Lowry carded a flawless 67.

American golfer Nick Watney withdrew from the event ahead of the second round after he tested positive for Covid-19, the PGA Tour confirmed.

Watney, who travelled privately to Hilton Head Island for the tournament and was not on the PGA Tour-provided charter flight, is the first member of the circuit to test positive for Covid-19.

The Tour said 369 individuals (players, caddies, essential personnel) underwent on-site testing prior to the start of the tournament, with zero positive results.

Simpson, who started on the back nine alongside DeChambeau and Davis Love III, hit 13 of 18 greens in regulation and made 186 feet worth of putts, including a 38-foot birdie at the par-four 18th.

He recovered in style after a bogey at the par-three seventh with a 19-foot birdie at his penultimate and a six-footer at the last following a brilliant approach shot from 114 yards.

DeChambeau, who has been crushing balls since returning from the PGA Tour's three-month Covid-19 hiatus with a bulked-up physique, bogeyed his opening hole but was flawless the rest of the way with eight birdies.