Woods and Mickelson shared the spoils at Medinah on Thursday

Playing in the traditional major winners' group with Geoff Ogilvy, the US Open champion, the American rivals were never quite at their very best.

Mickelson, the Masters champion, made a great start with two straight birdies but then lost his way a tad before picking up shots at his 14th and 16th.

Woods bogeyed the 10th, their 1st, but bounced back well to stay in the mix.

I was behind the eight ball early but you just have to keep plugging away Tiger Woods

Ogilvy, who also signed for a 69 that leaves them three off the lead, had the most eventful round of the trio, balancing seven birdies against two bogeys and a double-bogey.

But while Ogilvy's golf might have been more intriguing than his playing partners', all eyes at Medinah were on the clash of the game's two biggest stars.

And it was the 36-year-old Mickelson who drew first blood.

Woods, the Open champion and USPGA winner at Medinah in 1999, hooked his opening drive at the par-five 10th into the trees.

He had to lay up as a result, but then sent his 140-yard approach over the green and failed to get up and down.

"Lefty", on the other hand, smashed a 260-yard wood onto the green and two-putted for birdie. He then added another from five feet at the next.

(Tiger) is in his own world, I'm taking care of what I'm doing and we shake hands afterwards Phil Mickelson

But having given the world number two a three-shot start, the 30-year-old Woods, who is chasing a 12th major title to Mickelson's three, began to find his game.

The world number one birdied the 12th, 14th and 15th to reach the turn in 34, the same mark as Mickelson, who then bogeyed the short 2nd to fall back to one under.

But Mickelson, the defending champion, returned to two under with a birdie on the par-five 5th and both men picked up a shot on the long 7th to get to three under.

Woods, who has won the last six majors in which he began with a score in the 60s, said: "I was behind the eight ball early, but we all understand it's a long way and you just have to keep plugging away.

"We all did that and were grinding away. I kept the ball in play and made a couple of putts."

I had the best seat in the house Geoff Ogilvy

Mickelson, whose short-game coach Dave Pelz had sparked a pre-tournament debate by saying he thought his man was the better of the two when playing well, had two drivers in his bag just as he did in winning at Augusta in April.

"We both played OK, but had the chance to go lower and I'll try to get it ironed out on the range," said Mickelson.

"I've played a lot with Tiger (in all tournaments) and it's very enjoyable. He's in his own world, I'm taking care of what I'm doing and we shake hands afterwards."

Ogilvy, despite being ranked eighth in the world and a fine talent in his own right, admitted afterwards that at times it felt as though he was "just along for the ride".

And as thousands of fans at the Illinois course strained for a view of only Mickelson and Woods' second head-to-head at a major, the 29-year-old from Adelaide said: "I had the best seat in the house."