Mickelson - tied for the lead. (Getty Images)

With the eyes of the golfing world on him Justin Rose totally crumbled under the pressure of the Masters on Saturday.

But Paul Casey did anything but. Trying to become the first Augusta debutant to win since Fuzzy Zoeller in 1979 - and only the fourth ever - the 26-year-old from Surrey produced a brilliant 68 and will go into the final round in third place just two behind Americans Phil Mickelson and Chris DiMarco.

Rose, in stark contrast, collapsed to a nightmare 81 and now trails by nine - as does Tiger Woods after a second 75 of the week.

The dream of victory on only his second visit to the tournament turned into a horror story as 23-year-old Rose, two ahead at halfway, bogeyed his first three and six of his first nine holes.

That was three times as many as he had the first two days. It was sad to see.

By the time he reached turn in 42 Rose had fallen six strokes back and after he dropped further strokes at the 11th, 13th and 15th - that made it three bogey sixes in his round - he was down in joint 20th place.

DiMarco shot 68 and Mickelson 69 to take over at the top on the same six under par mark which Rose had reached after 36 holes.

Mickelson, of course, is trying to become the second left-hander in a row to win and to shake off the tag of "best current player never to win a major".

He has had no fewer than 17 top-10 finishes, including seven at Augusta. He has been third the last three years, but his putting and more cautious approach have put him in the position he is to put all his near-misses behind him.

It all started to go wrong for Rose when he drove into sand on the first and from there went over the green.

After failing to get up and down he thinned a pitch to the long second and flew into the crowd beyond the putting surface.

Again he needed three more and when he bogeyed the next as well he had already been overtaken.

That did not stop the bleeding, however. A six-foot par putt on the fifth dribbled past the edge of the hole - he could not believe it - and then a 10-footer on the next, again for par, was struck too firmly to take the break.

The tone had been set and he was unable to do anything about it. There was not a single birdie to lighten the gloom.

Not that he was alone to struggle. Twice winner Jose Maria Olazabal and German Alex Cejka, joint second at halfway, had 79 and 78 respectively.

Casey began the day six behind his fellow Englishman, but had moved two ahead of him with birdies at the third, fifth and ninth.

He came into the week with high hopes after paying an early visit three weeks ago.

"Everybody said that in terms of the majors this would be the one that would suit me most," said the 26-year-old, whose confidence was further boosted by a 10th place finish on his first appearance in the Players Championship a fortnight ago.

"It's scary because you then feel you have to perform well, but when I saw it I thought I would play well. I hit it high and go in with shorter irons than some of the other guys."

His back nine comprised eight pars and a 10-foot birdie putt at the par-five 15th. But he will hope a missed four-footer on the last after a brilliant shot from a fairway bunker does not cost him dear in the final analysis.

Casey added: "England are looking for another Masters champion and I would dearly love to fulfil that slot.

"I had a lot of fun out there. I think pairings count so much and Mark O'Meara was great to play with.

"I played some great golf, A couple of putts got away, but I was having a real ball. It's great to show the American crowds what I can do.

"I have not let the course get me down and I am really looking forward to tomorrow."

Ryder Cup captain Bernhard Langer had a 69 to move into joint fourth place with Ernie Els and South Korean KJ Choi on three under.

Forty-seven this August, Langer would take over from Jack Nicklaus as the oldest-ever champion, but even if he does he insists he will still not give up the captaincy and play at Oakland Hills in September.

"I don't know why people keep asking," he stated. "I have said I will not play."

Padraig Harrington gave himself an outside chance, shooting a 68 to move to level par after surviving the cut with nothing to spare.

Harrington chipped in at the 10th and finished in superb fashion with a five-iron to 10 feet.

An even better round came from Sweden's Fredrik Jacobson, a 67 for a one under aggregate. He is now eighth on his first appearance.