DiMarco - can he be caught? (Getty Images)

American Chris DiMarco held off a charging Tiger Woods on Saturday and remained on course to become the third successive first-time winner of the Masters at Augusta National.

But the 36-year-old, hoping to follow left-handers Mike Weir and Phil Mickelson into a green jacket, knows from bitter past experience not to count any chickens yet - especially with Woods in the mood he is.

Twelve months ago DiMarco was the joint 54-hole leader with Mickelson, but fell away to sixth with a 76. Four months later he was in a play-off for the US PGA championship, but saw Vijay Singh grab the title.

And after the weather problems on Thursday and Friday, DiMarco still has 27 holes to play on Sunday, not just 18.

Without a bogey since his opening hole he will resume on 13 under par, but Woods is only four behind after following a best-of-the-week 66 with a best-of-the-week front nine 31.

DiMarco has so far look unflustered, however.

He completed a second successive 67 to leave co-overnight leaders Luke Donald (77) and David Howell (69) trailing in his wake, then added birdies at the second, seventh and eighth.

"That was a day that you dream of," he said. "I kind of wish we were playing some more, but it's okay. I'm seeing the lines of the putts so well."

One of America's Ryder Cup debutants last September, DiMarco would have achieved the largest halfway lead in Masters history but for Dane Thomas Bjorn closing to four behind with two 10-foot birdies to go with earlier eagles at the 13th and 15th - only the ninth time that double has ever been achieved.

Bjorn is still in the hunt - perhaps the only other player in the hunt. His outward 34 left him eight-under, one behind Woods and five behind DiMarco.

Then there is a further four-stroke gap to Singh and Australian Rod Pampling, but Mickelson bogeyed the 10th just before the stoppage at 7.40pm local time and now has 10 strokes to make up.

Bjorn, of course, is the player who lost the 2003 Open at Sandwich from three ahead with four to play.

This time last year Bjorn was "fighting demons" and shot 80-77 round Augusta. He has also a best-ever finish of 18th in the event.

His two eagles were the result of a fairway wood to three feet and then a four-iron to within 12 inches.

"It's not that easy when you are out in the last few groups because the tension gets up," he said.

"But I've learnt to enjoy these opportunities when they come along. This is the finest tournament in the world."

Woods had been 33rd after an opening 74, but then suddenly found top gear.

After his superb 66 he reduced the 575-yard second to a 375-yard drive and towering iron - and almost made the first eagle of the week there.

Then he was just short of the green on the 350-yard third and pitched to four feet before finishing the nine holes with three more birdies - an approach to two feet on the seventh, a 10-foot putt at the next and then, after flirting with the trees off the tee, a pitch to three feet at nine.

Playing with Woods was David Howell, but after all the early promise of the first two rounds he double-bogeyed the first after a drive into the trees and a chip that came back to his feet, then bogeyed the third.

He did come back, but the pace was so hot he looks too far back to have a chance at two-under.

As does Donald, who hit back from a desperately disappointing 77 with three birdies in four holes on the back nine to climb into a share of seventh with Mickelson.

As for the other member of golf's 'Fab Four', Ernie Els was nowhere. The South African, who had a bad cold coming into the week, made the halfway cut with nothing to spare at four-over, then ran up a double-bogey seven on the 13th to be an incredible 17 shots adrift of DiMarco.

Meanwhile, an emotional Jack Nicklaus missed the halfway cut on nine-over following a 76 and said it was almost certainly his final Masters.

"I lost it there coming up the last," said the 65-year-old six-time winner, given a similar ovation to the one which greeted Arnold Palmer for his 50th and last appearance 12 months ago.

"I have the right to change my mind, but I don't think that's going to happen. I knew it was going to be my last time - it's too tough for me. I can't do this."

Nicklaus confirmed he will make his Open farewell at St Andrews in July.

The record halfway lead remains five shots by Herman Keiser in 1946, Nicklaus in 1975 and Ray Floyd a year later. All three went on to win.

At the start of the day Donald and Howell were both dreaming of becoming the first debutant to win since Fuzzy Zoeller in 1979, but Howell played the remaining 10 holes of his second round in two-over, while Donald fell away to a back-nine 40, going in the water at the 16th for a double-bogey five.

Howell's presence at the top of the leaderboard overnight had suddenly got Swedish television interested bizarrely.

That was because in his Friday press conference he was asked where was from and he replied: "Swindon in England." However, that was transcribed as "Sweden and England".

With Jesper Parnevik, Fredrik Jacobson and Joakim Haeggman all missing the cut, a Swedish television producer asked what Howell's connection with his country was and had to have the error pointed out to him.