It could well be the most exciting end-of-season tussle since Colin Montgomerie pipped Sam Torrance in 1995 with a three-foot par putt on the final green of the final event.

With one round left in the Volvo Masters money list, leader Casey remains favourite but only after Howell and Harrington wasted golden opportunities to apply maximum pressure.

Howell, who on Wednesday looked on the point of pulling out of the event because of a shoulder injury, has to finish in the top two and when he had five successive birdies early in his third round he was joint leader with Swede Henrik Stenson.

However, he three-putted the next, then covered the back nine in a disappointing 39 to fall back down into a tie for eighth place on level par, three behind the new surprise leader, Indian Jeev Milkha Singh.

Harrington, for whom a top three finish could be good enough with Casey only joint 32nd after his level par 71, moved into a tie for second spot when he turned in 33.

But then came three successive bogeys, two of them the result of three-putting, and that put the Dubliner on one over and joint 13th.

As for Karlsson, who needs first or outright second on Sunday, he is on level par with Howell after he mixed five birdies with four bogeys.

Lee Westwood was three clear in the tournament when he played the first six in two under against the three over of playing partner Stenson.

But Westwood then had a hat-trick of bogeys around the turn and slipped into a tie for second with Sergio Garcia and Swedes Stenson and Johan Edfors.

Singh, 147th in the world, is going for a Volvo double after capturing the China Open in April and he leads by one on three under following a 68.

Casey, who had been joint 35th at halfway, said of his round: "I thought I would move up a bit more. I didn't think it was easy and I was happy with that.

"I've not really crunched numbers, but I know I can maybe make Padraig finish second rather than third.

"Unfortunately the tournament is lost. There's nothing I can do about that. The first two days [when he was struggling with food poisoning] pretty much killed off my chances of being in contention.

"There's nothing I can do about it. Whatever happens happens. It would certainly be disappointing [if he cannot hold onto the number one spot], but I don't think it would be a crushing disappointment.

"If it does not happen I have plenty more chances. But I certainly want the Order of Merit before I hang up the clubs."

Howell was disappointed not to have capitalised on his opportunities, but remained hopeful. "It's exciting and I'm looking forward to it. I've given myself a chance and I definitely would have taken that Thursday morning.

"Golf is such a game of momentum. I was in a nice little zone early on, but then came the three-putt. Classic error, momentum lost.

"After being five under through seven it was obviously disappointing only to score 70, but would I have taken it before the start? Possibly."

At the 16th, Harringtonstood over an eight-footer for birdie and came off with a bogey. "Obviously I've got a difficult day ahead of me, " he said. "The 16th was probably the big miss. It really knocked me back.

"Four behind is not the end of the world, but I've put a lot of people between me and the lead and you've got to think somebody is going to shoot a decent score.

"It's not insurmountable, but when I was coasting along winning was a lot easier prospect than it is now."

Singh, making his debut in the event said: "I've seen the course on television so many times and hopefully I can keep going for one more day. If it happens, good. If it doesn't I've got another week."