Updated

By Mark Lamport-Stokes

THOUSAND OAKS, California (Reuters) - Former Masters champion Zach Johnson charged into a share of the lead in the Chevron World Challenge first round on Thursday.

In the absence of troubled tournament host Tiger Woods, the straight-hitting Johnson took advantage of ideal scoring conditions to fire a four-under-par 68 at Sherwood Country Club.

Johnson ended a day of dazzling sunshine and hardly any wind level with Britain's Ian Poulter, who held a two-shot lead over his 17 rivals in the elite field before double-bogeying the last.

Ireland's three-times major winner Padraig Harrington opened with a 69 to finish a stroke in front of Americans Jim Furyk and Stewart Cink and South Korean Yang Yong-eun.

"I wanted to come here fresh and that I am," Johnson told reporters after recording birdies on all four of the par-five holes. "I took 16 days off before I hit a ball after (the) Disney (Classic), and most of it was by choice. There were a couple of times I could have practiced but I just didn't do it.

"It's going well. I feel like my game is in a position good enough to win"

Poulter, feeling a little jaded after playing in Asia for the five previous weeks, was frustrated by his sloppy finish which featured a wild tee shot into trees and a three-putt on the 18th.

SIZZLING BURST

"It's four under par and I'm disappointed," said the Englishman who launched his round with a sizzling burst of five birdies in the first eight holes.

"Yeah I'm leading but I should have been way clear. I'm hitting my irons very, very well and I'm driving the ball in position. I'm giving myself a lot of chances.

"This is week six in a row for me so maybe a little bit of concentration slipping out there on the golf course might be the reason why I made three three-putts today."

"Then I'll come out tomorrow, hit more good golf shots and attack the flags," he added. "That's what I did today, I was attacking the pins."

European number one and world number four Lee Westwood briefly held a share of the lead with Poulter at five under before dropping four shots in the last five holes for a 71.

The absence from Sherwood of 14-times major champion Woods, who pulled out of the event citing injuries from a car crash outside his Florida home last week, has been a major talking point for the fans this week and Johnson said the atmosphere on Thursday was noticeably different.

"I think there's less of a buzz, as chaotic as it really might be if he had been here," Johnson said.

"There's certainly less media here."

(Editing by Ian Ransom/Greg Stutchbury)