SHANGHAI (Reuters) - Japan's Hideki Matsuyama made light work of tough conditions at the WGC-HSBC Champions with a sparkling seven-under-par 65 to surge ahead of a stellar field after the second round at a wet and windy Sheshan International Golf Club on Friday.

World number three Rory McIlroy rediscovered his touch on the greens after struggling with the putter en route to a first-round 71, sinking seven birdies for a 66 to close within six shots of the lead going into the weekend.

The in-form Matsuyama started with a bogey and dropped another shot at the ninth but nine birdies gave him a three-shot lead over reigning champion Russell Knox and American Bill Haas on 13-under for the tournament.

"Coming here, I was a little bit nervous again thinking, maybe it's not going to be a good week for me," said the world number 10.

"But then I decided, 'oh, wait a minute, let's just have fun this week'. It's made a difference."

Matsuyama carded 66 in Thursday's opening round but went one better on Friday thanks to an error-free back nine, closing out the day's lowest round with a stunning approach shot to birdie the final hole.

Early-pacesetter Rikard Karlberg of Sweden, who shot a first round 64, ended up with a 75 after five bogeys on the front nine, while Knox continued his strong start with a measured 68.

The Scot, who won on his debut at Sheshan last year, got his first birdie at the second before dropping a shot at the third. He steadied the ship by picking up shots on the fifth, seventh and eighth and another on the 12th.

American Rickie Fowler was just one shot off the pace after the first round but slumped to a 73 on Friday, while compatriot and world number two Dustin Johnson also struggled.

The U.S. Open champion started the day at two-over and things did not get much better as he dropped six shots, including a double bogey at the 10th hole, to offset an eagle at the par-five 14th and card another 74.

(Reporting by Simon Jennings in Bengaluru, editing by Nick Mulvenney)