Tony Finau moved into a one-shot lead during a roller coaster second day of the WGC-HSBC Champions at Sheshan International Golf Club.
Patrick Reed entered the day at eight under and he stayed there after turning in level par with Finau one shot ahead but that did not tell the full story of some thrilling action in Shanghai.
At one point Finau and Reed were four clear of the rest of the field and shortly after that Finau was three ahead of Reed, with both men coming back to the pack.
A birdie on the 14th meant that Finau was one ahead of Reed with four to play, with another American in Xander Schauffele at seven under.
Defending champion Justin Rose and Americans Keegan Bradley and Patrick Cantlay were three shots off the lead.
Finau got within one of the lead as he took advantage of the par five second and a 15-footer on the fourth gave him a share.
The man from Utah then got up and down from the sand on the driveable par four seventh, holing a ten-footer to hit the front on his own.
Reed was among the late starters but it did not take him long to reclaim a share of the lead, playing a wonderful short pitch to set up a birdie on the second.
Finau birdied the par five eighth to get to double-figures but Reed's approach to the third was to eight feet and the duo were tied once more and four ahead of the chasing pack.
Reed recovered well from a poor tee-shot on the fifth but missed a short one and when Finau holed a ten-footer on the tenth, he led by two.
The Masters Tournament champion 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.
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.
Rose birdied the second and holed an eight-footer at the third before making another birdie on the eighth.
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.
Bradley was having a wild round, birdieing the second, fourth and fifth but making a double-bogey on the eighth to turn in 35. He birdied the tenth and brilliantly chipped in at the 11th but bogeyed the next before picking up a shot on the 14th.
Kiradech Aphibarnrat, Tommy Fleetwood, Ian Poulter, Pat Perez and Emiliano Grillo were four off the lead.
