Despite struggling off the tee, Phil Mickelson enjoyed a good start at the Barclays Singapore Open today, carding a three-under-par 68 to share second spot midway through the opening round.

Strong iron play saw the 37-year-old pick up six birdies to leave him two strokes behind clubhouse leader Gavin Flint of Australia after the morning session at Sentosa Golf Club's Serapong Course.

But the American, who was joined on three under by Korea's KJ Choi, was keen to talk to swing coach Butch Harmon after having difficulty with his driver and three wood.

"I scored well, I made some good putts and I made some good iron shots but my driving was terrible," said Mickelson, who saw his card blotted by a double bogey at the par-four third and a bogey two holes later.

"It's the worse it's been since I started working with Butch Harmon. I'm going to give him a call as soon as I've finished.

"This course is very challenging tee to green, the fairways are tight and I drove it very poorly today. I was lucky to escape with a three-under-par round but I feel that if I can get my driver and three wood turned around, I should be able to have a good remaining three days.

"I'll just talk to Butch and see if we can get this ironed out for tomorrow."

Although it was Mickelson's first round of golf in south east Asia, the American felt comfortable with the warm and humid conditions.

"I don't mind the heat because your body is looser and also when it's hot, the ball flies straighter and further, so it helps with scoring conditions. I didn't expect the course to be this difficult. I think that this is a (US PGA) Tour-calibre golf course and the set up is a Tour-quality, tough test of golf."

Flint, who has a Singaporean mother, was delighted to find himself at the top of the leaderboard after firing five birdies for a bogey-free, five-under-par 66.

"I'm definitely very pleased with my performance this morning. I hit the ball really well and putted well also," said the 26-year-old Brisbane resident.

"It feels like a national Open to me. I had my mum and a few other friends out there supporting me this morning and to be able to stay at home is very good."

Choi shot five birdies, including three straight on his back nine, to find himself tied with Mickelson, with Anthony Kang of the United States and Gary Simpson of Australia a further stroke back on two under.

Singapore's Mardan Mamat should also have been in contention after shooting a 69 but the local favourite was disqualified after wrongly signing for a round of three under.

Defending champions Adam Scott and world number 13 Vijay Singh were on one-under 71 while Darren Clarke was a further stroke back after a level-par opening round.