WGC Cadillac Championship, Florida par=72: -9 H Mahan (US) -8 M Kaymer (Ger), F Molinari (Ita) -7 N Watney (US), M Laird (Sco), M Kuchar (US), R McIlroy (NI) -6 A Baddeley (Aus), A Scott (Aus) D Johnson (US)
Selected others:-5 L Donald (Eng), E Els (SA), P Harrington (Ire) -3 P Casey (Eng), R Ishikawa (Jpn) E L Westwood (Eng), T Woods (US), P Mickelson (US)
Mahan's lead has been cut to one but the American still heads the field in Miami
World number one Martin Kaymer moved to within one shot of leader Hunter Mahan after two rounds of the WGC Cadillac Championship in Florida.
American Mahan marched into a four-shot lead but two late bogeys saw him card 71 for a nine-under-par total while German Kaymer birdied 17 to post 70.
Back-to-back birdies for Francesco Molinari on the 17th and 18th drew him level with Kaymer on eight under par.
Scot Martin Laird and Rory McIlroy are both in contention at seven under.
Mahan looked set to finish the day comfortably clear of the chasing pack after birdies on the 6th, 10th and 12th holes but he gave two shots back on the 14th and 16th.
However, Mahan is optimistic that he can hold off the challenge of the European players.
It's been mostly about getting confidence in myself and I've started to believe I could be a top-10 player in the world
"I'm still in a good position for the weekend, I think the conditions suit my game," he said. "I can't be too disappointed with the last two days. I just need to keep driving well and keep putting well and I'll have a chance."
Kaymer, just two weeks into his reign as world number one, did not drop a shot on his way to a solid two-under par 70.
The German said he was "very happy" with his performance since becoming the best-ranked player in the world.
"After the PGA Championship [his first major win last August] a lot of people thought this may be the end of my career, especially in Germany," he added.
"A lot of people were expecting a lot from me, but they were not expecting that I could win a major, and once I reached the top everybody was surprised.
"I was surprised too and nobody really thought I can keep up that level. That's why it was even more important for me to keep winning.
"I love so much to be in contention every week. That is what golf is all about and that is why I practise so hard - to be in that position as much as possible.
"I'm the number one in the world for at least two weeks. Hopefully if I keep playing the way I do then another week. And then we'll see.
"I don't really worry about the world rankings. I think you only have to worry if you play bad golf."
Italy's Molinari enjoyed a late flourish, climbing to joint-second on the leaderboard with a four-under-par round of 68.
Despite a double-bogey five on the 13th, Laird's luck seemed to be in as the Scot recovered to post a score of 70 that sees him on seven under for the tournament.
Laird, based in the United States since his college days and a winner on the PGA Tour two years ago, included a 45-foot putt on the short ninth and a 57-foot chip-in at the 16th in his 70.
"I've been playing good for a while," said the Glaswegian. "It's kind of easy in a way when you sneak under the radar and quietly go about your business. It's been mostly about getting confidence in myself and I've started to believe I could be a top-10 player in the world."
Australian Aaron Baddeley enjoyed the round of the day posting a 66 and, along with compatriot Adam Scott and American Dustin Johnson, remains within touching distance of the lead on six under par.
Lee Westwood twice found the water on the long eighth and the resultant double bogey seven blighted his card as he posted a 74 to fall back to level par for the tournament.
But it was a slightly better day for fellow Englishman Luke Donald who remained on five under, despite bogeys on the 15th and 16th.
Former world number one Tiger Woods continued to struggle for form, posting a 74 to join Westwood on level par.
The 14-time major winner had two embarrassing moments - hitting a woeful 122 yard drive on the second hole, which did not even reach the ladies' tee, and then skying a three wood off the 14th tee, making only 188 yards.