Tony Finau will take a three-shot lead into the weekend at the WGC-HSBC Champions after firing a 67 on a day of twists and turns at Sheshan International Golf Club.
The American entered the second round two shots behind overnight leader Patrick Reed but soon overhauled him and led by three before an unfortunate double-bogey on the 11th.
Three birdies in his last five holes then moved the 29 year old back to 11 under, three shots ahead of Masters Tournament champion Reed, defending champion Justin Rose and reigning Race to Dubai champion Tommy Fleetwood.
American Xander Schauffele was then at seven under, a shot ahead of countryman Patrick Cantlay.
Fleetwood and Reed are currently second and third respectively in the Race to Dubai Rankings presented by Rolex as they look to chase down Francesco Molinari, while Rose could go back to the top of the Official World Golf Ranking should results go his way over the weekend.
Finau made his Ryder Cup debut for the United States in the recent defeat at Le Golf National and is looking for his first European Tour win in just his 20th appearance.
He played his first regular event in a decade at the Alfred Dunhill Links Championship earlier this month and arrived in Shanghai with some momentum after a top ten in Scotland.
"I'm really pleased," he said. "I played nicely and was happy with the way I finished. I was pleased to make a few birdies coming down the stretch.
"There's a lot of great players here that are looking to chase me down. I've got to stay in attack mode, continue to make birdies and if I limit the mistakes, I think it will be a good weekend."
Finau took advantage of the par five second, holed a 15-footer on the fourth and then got up and down from sand on the driveable par four seventh to take the lead.
I've got to stay in attack mode, continue to make birdies and if I limit the mistakes, I think it will be a good weekend - Tony Finau
Reed played a wonderful short pitch to set up a birdie on the second but Finau edged back ahead as he birdied the par five eighth before Reed holed from eight feet on the third.
At that point the leading duo were four clear of the field but Reed bogeyed the fifth and a Finau birdie from ten feet on the tenth handed him a two-shot lead.
Reed found water on the sixth to hand Finau a three-shot advantage but the leader got a nasty bounce off a sprinkler-head on the 11th to go over the back of the green and failed to find the putting surface with his third, eventually surrendering a double-bogey.
Another bogey came on the 13th after Finau found a bunker with his second meaning the lead was back at eight under where it had started the day.
A birdie after getting on the par five 14th in two then handed Finau a narrow lead and better was to come over the closing stages. He hit a brilliant approach into the 16th and got on the green at the par five last in two for a pair of birdies and a three-shot advantage.
The lead was four when Reed bogeyed the 14th but he got up and down from the side of the driveable 16th and nearly finished with a sensational birdie after putting his third on the last to within six feet after finding water off the tee.
Rose birdied the second and holed an eight-footer at the third before making another birdie on the eighth to turn in 33. A stunning approach to six feet on the 11th moved him closer before he birdied the last in a bogey-free 67.
Fleetwood birdied all four of the par fives and a stunning approach into the 11th brought another gain with a single dropped shot on the fourth.
Affiliate European Tour Member Schauffele started with seven pars but birdied the eighth before giving the shot straight back after finding sand. He got back to seven under with a gain on the 11th but once again dropped a shot on the 16th before picking it back up on the last.
Cantlay recovered from a bogey on the first with birdies on the third, fifth, sixth, eighth and ninth to turn in 32. He then bogeyed the 14th but picked the shot back up on the 16th.
Belgian Thomas Pieters matched the lowest round of the week with a 64 to sit at five under alongside Kiradech Aphibarnrat, Keegan Bradley, Emiliano Grillo, Pat Perez and Kyle Stanley.
