Robert Karlsson rallied from shaky start while Phil Mickelson remained in contention despite a roller-coaster ride in the rain-hit first round of the PGA Championship.

Sweden's Karlsson and India's Jeev Milkha Singh each shot two-under 68 and are the co-leaders in the clubhouse on Thursday at the Oakland Hills Country Club.

The 38-year-old Karlsson got off to a rough start with a double bogey on the opening hole. But the six-foot-five Karlsson refused to wilt, posting four birdies on the next six holes in the $7.5-million event.

"The shots can only come when I am standing on the first tee and not too afraid to go out and meet a very tough golf course," said Karlsson.

Both Karlsson and Singh teed off in the morning session and before a thunderstorm resulted in a 25-minute delay for the afternoon group.

The 18 players who couldn't finish their round on Thursday due to darkness will be back on the course Friday morning to complete the first round.

Spain's Sergio Garcia is part of a group of four players in the clubhouse at one-under while Mickelson, Anthony Kim and Rod Pampling are just two shots adrift of Karlsson and Singh after shooting even-par 70.

Co-leader Singh had to put a nagging ankle injury aside in order to shoot his 68.

That seems to be a recipe for success in the majors this year as Tiger Woods (knee) and Padraig Harrington (wrist) won their majors while playing hurt.

"I have been suffering with a little tendon running through my ankle on the right foot and it is very painful," Singh said. "I have been wearing a brace for the last four weeks.

"It is getting better but if I hit one of those shots out of the rough then I am back to square one."

The 36-year-old Singh posted an eagle on the par-five second hole and then rolled in three more birdies to go with 11 pars.

Pre-tournament favourite Mickelson started his round with a pair of bogeys but recovered to finish with an even-par 70.

With two-time defending champion Woods sidelined after undergoing season-ending knee surgery, the door is open for someone like Mickelson to try and win another major.

Mickelson played in a group with two other former PGA Champions Davis Love (77) and Rich Beem (73). It wasn't quite the mega threesome of Woods, Mickelson and Adam Scott at the US Open in San Diego but they did provide some thrilling shots for Detroit-area golf fans.

Starting from the 10th tee, the three-time major winner Mickelson made back-to-back birdies on holes number 16 and 17 then made bogey on number 18.

He finished with five birdies and made bogey on the same number of holes. He parred just two of his first nine holes.

"I am just happy to have shot even par today," Mickelson said. "I think after the start, bogeying the first two holes, I thought I was pretty good to hang in there."

The left-handed American has two wins this season (Northern Trust Open and Crowne Plaza Invitational) and is looking to turn a solid year into a special one with his first major win of 2008. He tied for 37th at last year's PGA Championship in Tulsa.

One of Mickelson's bogeys came on his ninth hole of the day, the par-five 18 as he missed a six-footer for par.

Mickelson wasn't the only player having problems on the green at 18 which proved to be the most difficult hole of the day.

Playing partners Camilo Villegas (74) and Anthony Kim (70) both three-putted there.

The rain interrupted a strong start by South Africa's Retief Goosen who was two-under through 11 holes. Goosen made birdie on three of his first four holes after drawing an afternoon tee time.

But he couldn't regain the touch when play resumed, making bogey on four of his final seven holes to finish at two-over 72.

AFP