US unless stated -9 Justin Leonard, Vijay Singh (Fij) -8 Briny Baird, Darren Clarke (GB), Ernie Els (SA) -6 Chris DiMarco -5 Stephen Ames (Can), KJ Choi (Kor), Padraig Harrington (Irl), Chris Riley Clubhouse scores

The duo are on nine under, one clear of Northern Ireland's Darren Clarke, world number two Ernie Els and unheralded American Briny Baird.

Leonard carded a three-under 69 on Friday, while Singh, the world number three, went one better.

Els had held the lead on his own at 10 under after 10 holes, but two bogey-sixes dragged him back.

The South African is desperate to land a big prize this year after second-place finishes at the Masters and Open, as well as another missed opportunity at the US Open.

Singh, who won this event in 1998, joined Leonard, the 1997 Open champion, on nine under when he converted a birdie chance on the par-five 16th.

But the 41-year-old Fijian's progress up the leaderboard went almost unnoticed amid the drama surrounding playing partner Tiger Woods' efforts to make the cut.

I certainly didn't expect to see so many players under par - and I am very pleased with the score I am on Darren Clarke

The world number one had not missed a weekend since turning professional in 1997, but with six holes to play he was three over par, two shots off the projected cut.

The American is nothing if not a fighter, however, and three birdies in five holes saw him get back to level par. Woods has now made 129 cuts in succession.

Clarke, the overnight leader at seven under, endured an eventful second round.

The Ulsterman, who turns 36 on Saturday, posted a double-bogey seven after visiting three of the many bunkers that flank the 618-yard 11th, his second hole.

Academy: If Darren Clarke could...

But Clarke refused to buckle, and four birdies over the next 12 holes got him back to nine under.

A bogey at the sixth, his 15th, was followed by a huge birdie putt at the seventh.

Sadly, Clarke then missed a short par putt at the eighth and an eight-foot birdie putt at the ninth to reach the clubhouse on eight under.

Clarke said: "After the double bogey I tried not to get too aggressive, then got it going a bit and then made a couple of mistakes.

I'm just trying to win a golf tournament - if it happens to be a major, great Briny Baird

"I certainly didn't expect at the start of the week to see so many players under par - and I am very pleased with the score I am on."

Baird was the first man to reach that mark, and with the overnight leaders all starting in the afternoon he enjoyed the clubhouse lead for most of Friday.

Still chasing his first PGA Tour win, Baird has until now been more famous for his unusual putting technique.

But after 10 different winners at the last 10 majors, nobody would be surprised if another unlikely winner emerged at Whistling Straits.

"I'm just trying to win a golf tournament. If it happens to be a major, that's great," said Baird.