USPGA TOUR:VIJAY SINGH is not ready to concede his Arnold Palmer Invitational title without a fight.

The defending champion shrugged off a recent bout of food poisoning to take the clubhouse lead during the second round at Bay Hill in Orlando.

He carded 65 to post a nine-under-par 131 halfway total, two strokes clear of Carl Pettersson (65) and three in front of Lee Westwood (68) with half the field back in the clubhouse.

"I hit the ball really good off the tee, gave myself a lot of birdie chances and also helped by chipping in twice as well," said the 45-year-old from Fiji.

"I'm not doing anything special, not doing too much wrong either, just cruising along."

Singh said he lost nearly 20 pounds last week due to a severe bout of food poisoning he contracted on his way back to Florida after the Johnnie Walker Championship in India.

He was in such a bad state with dehydration that he even went to hospital, where he was hooked up to an intravenous drip.

"I thought I was going to pull out of this tournament but on Friday I started to feel a little better," he said.

Tiger Woods, seeking to win his sixth consecutive title, is seven shots back after a second round 68 for a two-under-par 138 total.

Westwood was frustrated not to make an even bigger splash and insisted "it was there to be taken".

The Ryder Cup star stands at six under par - three strokes behind leader Vijay Singh with half the field in the clubhouse.

But despite a largely trouble-free round for the 34-year-old, he could not help looking at what could have been as he enjoyed relatively benign conditions in otherwise trying weather.

Westwood was generally satisfied with his round of 68 but could not resist picking a few holes in his game.

The Englishman acknowledged he coped well when the winds did arrive late in his round but was less than satisfied with his approach play and believes he could have mounted a serious bid for top spot.

"It was there to be taken, the course. I thought for the morning players, the wind only really got up on our last three holes, one of which I birdied and played pretty solidly all day around.

"I hit one bad drive off eight into the right-hand trees and it wasn't that far off line, but was never really in too much trouble all day. I hit a few long drives, as well but just didn't hit my iron shots close enough to the flags.