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 start, had a late tee time to follow his even par round of 70 from the opening day.