Padraig Harrington got off to a shaky start in his pursuit of a first order of merit title this afternoon, a two-over par 71leaving him seven shots off the lead at the Volvo Masters.

The Dubliner requires at least a top three finish in the season ending event at Valderrama to have any hope of overhauling Paul Casey at the top of the standings but despite a bright start, was unable to impose himself at the business end of the leaderboard.

Casey was even further off the pace after struggled to an opening five-over-par 76. The round left him joint 43rd of the 54-strong field and 10 adrift of leader Jose Manuel Lara, but still in pole position.

That is because Harrington, who needs a top-three finish, is only 30th and David Howell and Robert Karlsson, who have to be first or second on Sunday just to have a chance, are 14th and seventh respectively.

All the attention on the eve of the event had been on third-placed Howell, who was "50-50 at best" just to tee off because of his shoulder problem.

But while Howell was delighted with a one-under 70 in the circumstances, Casey, who had suffered stomach cramps on the course, was more concerned about his health than his score.

"I just want to get inside," was the first thing he said after signing his card. After a visit to a toilet, Casey added: "It was the worst I've ever felt on a golf course. I was up a few times last night and although it was not too bad starting out I was not feeling good.

"Then it just got worse and worse. My stomach really cramped up on the 10th tee and on the 11th I got an injection to stop the nausea and a pill to solidify the rest.

"It feels like 'flu because my whole body is aching. In any other circumstances I don't think I would have kept playing, but I'm not a fan of pulling out and I think I should keep going as long as I can or a doctor says otherwise.

"I wasn't even thinking about the score. I'm a long way back, but I'll just try to get under par by the end of the week."

On several occasions he crouched down and leant on his golf bag for support, but he soldiered on and still managed to beat nine others, Ryder Cup team-mate and eight-time European number one Colin Montgomerie among them.

While obviously feeling sympathy for his playing partner's plight, Harrington was hoping to put as much distance as possible between them to boost his money list chances.

If Harrington wins this weekend there is nothing Casey can do to stop him being crowned, but the Dubliner fell back from two under after seven to two over.

"I should have been four under after five," he said. "I hit a few bad putts and wasn't trusting my reads after that. There you go - it goes like that some days. It was obviously a tough day for Paul. He was struggling to get round and nothing seemed to go right for him either.

"I wouldn't think it had a detrimental effect, but it's nice to see putts going in and neither myself or Paul holed any."

Howell had six birdies, however. Having passed a fitness test he set off with a 12-footer and finished off a three-under inward half of 33 by sinking a bunker shot of over 20 yards on the last.

"Crazy game - I'd hit a dreadful second shot," he said. "Lots of muscles are still tight and sore, but I wasn't feeling any pain and I've got to put it down as a great day.

"I'll get some more ice and physio now and I'm fairly hopeful I will get through the week now.

"I would have been very disappointed not to tee off this week. I think I would have gone to the end of the Earth to give it a go and to score 70 is as good as I could have expected.

"I'm certainly pleased to be in touch with the leaders. "

Lara, hoping to become the first Spanish winner of the title since Miguel Angel Jimenez in 1999, birdied the final two holes to move a stroke ahead of Graeme McDowell, Australian left-hander Richard Green and Swede Niclas Fasth, winner last Sunday of the Mallorca Classic.