Louis Oosthuizen and Adam Scott fired matching 7-under 65s on Thursday to share the opening-round lead at the WGC - HSBC Champions.

Oosthuizen had a bogey-free round that he capped with two birdies in his last three holes, while Scott had two birdies and an eagle in his last three holes on the Olazabal Course at Mission Hills Golf Club.

Phil Mickelson and Masters champion Bubba Watson both carded 6-under 66s. They were joined in third place by Peter Hanson, who won last week in Shanghai, and Shane Lowry, who bogeyed his final two holes on Thursday.

Like the two leaders, Mickelson started on the back nine and he birdied his first two holes. After three pars, Mickelson birdied the par-5 15th. He parred five in a row around the turn.

The 2007 and 2009 champion birdied the par-5 third. Mickelson closed with an eagle on the par-5 ninth to end one back.

Dustin Johnson and Prom Meesawat share seventh place at minus-5, while Luke Donald headlines a group of five players tied at 4-under 68.

Oosthuizen birdied the 11th, but that was his only birdie in his first five holes. He birdied the par-5 15th and par-4 18th to make the turn at minus-3.

The 2010 British Open champion made it two in a row with a birdie at the first. He came back with a birdie on the third to get to 5-under. The South African birdied two of his last three holes to grab a share of the lead.

"I don't think I saw a really low number out there, but once you look at the leaderboard and see the guys are firing it up, all of a sudden you started seeing birdies," said Oosthuizen, who lost to Watson in a playoff at the Masters. "I played well. I made five birdies on the par-5s, and that got the round going."

Scott also birdied No. 11 to get his round going. He dropped in back-to-back birdie efforts at 14 and 15. Scott stumbled to a bogey on the 17th and headed to the front nine at minus-2.

The 2011 WGC-Bridgestone Invitational winner birdied the third to move back to 3-under. After three straight pars, he caught fire.

Scott birdied Nos. 7 and 8 before making a 12-foot eagle putt at the last to join Oosthuizen in the lead.

"It was a solid day that all of a sudden turned into a really good day. I hit a lot of good shots, and they ended up finishing close on the last couple holes and I took advantage of that," Scott stated. "With five par-5s, it sets up well for my game, and the plan is to just take advantage of the fives and hopefully hang in there with the leaders all week."

NOTES: Oosthuizen owns five European Tour victories, while his British Open crown is his only PGA Tour win...Scott has eight wins on both the PGA and European Tours...Last year's winner Martin Kaymer mixed six birdies and two bogeys in a round of 4-under 68, which left him tied for ninth...There are 16 players from this year's Ryder Cup in the field and nine are in the top 18 on the leaderboard.