It became a tale of the Thin Man and the Bear when the US Masters reached the halfway stage here yesterday. While David Duval swept to the top of the leader-board with a sparkling 65 for a six-under-par 138, Jack Nicklaus was doing remarkable things for a 60-year-old grandfather.

After a second round of 70 for 144, there he was mouthing the words: "I've still got a chance to win the tournament."

Had it been anyone other than the winner of 18 major titles, one might have been seriously tempted to alert the nearest psychiatric unit.

But this was Nicklaus. And he was on his favourite stomping ground in glorious, sunny conditions which were almost guaranteed to dispel even the most stubborn arthritic pain.

On the other hand, Duval of the lean and hungry look would positively welcome a physical challenge. On this occasion, however, he settled for the usual leisurely pace of a five-hour round while carding a stunning back nine of 30, which included an eagle at the long 15th.

In considerably kinder conditions than on Thursday, Vijay Singh had seven birdies on the way to a 67, the same as Ernie Els, to leave both a stroke behind the clubhouse leader. Phil Mickelson joined them in the hunt, with birdies at the 11th, 13th, 14th and 15th to be six under par and level with Duval at that stage, before the left-hander let one slip at the 16th to finish with a 68 and lie at five under.

Ireland's challenge remained largely in the formidable hands of Darren Clarke, who shot seven birdies on the way to a 71 for 143.

But Padraig Harrington also had a strong day, firing a three-under-par 69 to finish at 145, one over, and by no means out of touch of the leaders. The Dubliner started brightly with birdies at the first, sixth, seventh and eighth to be level-par for the championship.

As Clarke had done earlier in the day, however, Harrinton proceeded to suffer a mid-round crisis, when a double-bogey on the ninth was followed by bogeys at the 10th and 11th. But like his colleague, he, too, rallied later on the back nine, carding birdies at the 13th and 14th.

And he finished the job in fine style by holing a 12-footer for birdie at the last to set up a potentially fascinating debut weekend.

Away from the excitement generated by the leaders, the grapevine carried decidedly unhappy tales of the Tiger. After an opening 75 which he had accepted as "fine", the world number one reached the turn yesterday in 34 to be one under par overall. But he then slipped into the danger-zone with bogeys at the 10th and 11th.

With the 10-shot rule applying, Duval's successful 12-foot birdie putt on the 18th spelt the end for defending champion Jose-Maria Olazabal, who shot 77 for 149. The Spaniard also birdied the last, but, unfortunately for him, irreparable damage had already been done by a seven, two sixes and a five in an opening nine of 42.

"It was just a terrible day on the greens," said the dejected champion. "It has never happened to me before and what's makes it really depressing is that it was all my fault. If you don't make putts on this course, you're obviously in trouble."

Colin Montgomerie, who shot an admirable 69 for 145, found a spectacular solution to that particular problem. The Scot holed out an eight-iron second shot of 140 yards for an eagle two at the 435-yard fifth.

Another European, Bernhard Langer, is in contention for his third Masters after a second successive 71. Retaining the ability to play difficult courses well, Langer made his move with a birdie at the long 13th, which he had eagled on Thursday. And he also birdied the 14th in a back nine of 34.

Duval, who shot a closing 67 to share second place here in 1998, has set his heart on this particular title. "I had a very good opportunity two years ago, but I don't believe I gave it away," he said. "Mark O'Meara birdied the last two holes to go past myself and Freddie (Couples).

"I've played well so far this week, but my goal is to be leading on Sunday afternoon," he added. "I have high expectations of myself and I was really pleased with the way I played today. I hit virtually every green."

After an outward 35, in which he birdied the long second, Duval sank a 12-footer for another birdie at the short 12th. He went on to sink a seven-footer for birdie at the 14th, and then moved centre-stage with an eagle on the next. From a five-iron second shot, his ball finished 10 feet below the hole - the perfect position from which to make a strong, positive stroke.

From there, Duval protected his score by two-putting from off the right side of the 16th green for par. And he went on to birdie the 17th, where he wedged to four feet, and the 18th, when a 12-footer found the target.

As a 14-year-old, Duval was at Augusta on the Thursday and Friday in 1986 when Nicklaus captured the title for a sixth time.

Now the legendary champion was saying: "I feel fine physically and I've no problem with concentrating. Where winning a golf tournament is concerned, I believe that age doesn't have much to do with it, if you've got your nerve. And my nerve is fine."

Wind, rough and notoriously slippery greens didn't intimidate him. In 36 holes so far, he has carded only four bogeys and nothing worse. And he claimed to have holed nowhere near his share of putts. Amazing.