A meal of crab which left him feeling ill may have cost Darren Clarke his chance of a third European Tour victory. But if the Portuguese Open trophy does not go into the big Irishman's trophy cabinet this year it will not be through lack of determination after he clawed his way back into contention in the face of desperate odds.

After spending the night mainly in the toilet with food-poisoning, Clarke called a doctor and it looked as though his tournament was over, despite the fact that he had held the overnight lead after a superb seven-under-par 66 in the first round.

But despite tottering to the tee on weakened legs, and then suffering the despair of falling nine strokes behind new leader Wayne Riley, Clarke brilliantly turned his day right at the end.

Three birdies in the last nine holes, two of them agonisingly close to eagles, brought him right back into this event. He is now six strokes off the lead on six under par after his battling 74. "It was so very disappointing after my 66 of the first round," said Clarke with crushing understatement after a four-putt and two three-putts had left him wilting at four over par by the turn. "I'd gone down the range to practise after I finished on Thursday and I was hitting the ball just as I wanted to.

"Then I get a really bad dose of food poisoning. I think it was a crab I ate in one of the local restaurants and I was really, really ill all night. "I didn't think I'd even be able to play. This course demands such a lot of you. I just tried to swing, tried to play but things were bound to go wrong. The four-putt and three-putts were all down to lack of concentration and energy."

Now the fight is on to catch Riley, who went to 12 under par after a 66, two strokes ahead of blazing Scot Paul Lawrie who posted a 64. England's David Gilford and Peter Mitchell are a further stroke back in third place.

Clarke's doggedness left him one shot better than Des Smyth as top Irishman. The Drogheda player turned it on early, picking up three birdies in the first four holes and three in succession around the turn, including a 40foot putt on the 10th after he hit a tree.

At the short 13th his ball dropped into the lake, but he whipped off his shoes and socks to pitch out from the water to 15 foot and sank the putt to save par! He did, however, bogey the 14th, and finished with 68.

Only two other Irishmen made the level-par cut. Raymond Burns produced an exemplary four birdies and no bogeys for a 69 and a one under par 145, the same as rookie Cameron Clark, whose two closing birdies got him in for his first weekend action.

Eamonn Darcy picked up three successive birdies and five in the first eight holes, but a seven on his ninth, when he was twice bunkered, scuppered his chances. He ended with a 70 and one over par.

Christy O'Connor Jnr suffered the same fate, one over after 73. Francis Howley, 75, and David Higgins, 76, were three over.