Justin Rose and Trevor Immelman take charge at Augusta

AUGUSTA, Georgia (Reuters) - Britain's Justin Rose reeled off six birdies in eight holes to share the first-round lead at the U.S. Masters while Tiger Woods labored to stay in touch on Thursday.

Rose, who led after the first two rounds in 2004, shrugged off two early bogeys to fire a four-under-par 68 in bright sunshine on a soft Augusta National layout playing extra long.

The 27-year-old launched his sizzling run at the par-three sixth before ending the day level with South African Trevor Immelman, who missed a 10-footer at the last for a 67.

Britain's Lee Westwood, four under with two holes to play, bogeyed the 17th in fading light on his way to a 69 and a tie for third with Americans Brandt Snedeker and Masters debutant Brian Bateman.

World number one and four-times champion Woods, seeking his 14th major title, parred the first 12 holes before going bogey, bogey, eagle on his way to an opening 72.

Rose, who tied for fifth at last year's Masters, was delighted to rebound from his faltering start.

"I didn't feel that comfortable out there on the course but I made a great swing into six, hit it to five or six feet," he told reporters.

"From the tee, it looked like I was close then I went up there and it was a little farther than I would have liked. I hadn't putted well the first few holes, but making that slippery little putt settled me down."

Rose, who clinched the European Tour order of merit for the first time last year by winning the season-ending Volvo Masters, refused to get carried away with his first-round effort.

"Being in the lead on day one, it really means nothing," he said. "You can't win the tournament the first day, you can only lose it. I haven't lost it, so it's a great day."

CALENDAR SLAM

Woods, who has set his sights on becoming the first professional to achieve a calendar slam of the four majors, scrambled to stay level after 12 holes before bogeying 13 and 14.

However, he chipped in from behind the green to eagle the par-five 15th before parring the last three holes to finish four strokes off the pace.

"I didn't really get anything going my way today," the 32-year-old American said. "I played a lot better than what my score indicates. I hit a lot of good putts, nothing really went. I just had to stay patient out there.

"The way the golf course plays now, you don't really shoot low rounds here any more. You've just got to plod along. It's playing more like a U.S. Open than it is a Masters."

Britain's Ian Poulter spectacularly aced the par-three 16th on his way to an opening 70 in his fourth Masters appearance.

The 32-year-old Poulter holed out with an eight-iron from 169 yards to get to three under before slipping back with a bogey-par finish.

"I flushed it," the seven-times European Tour winner said of his ace. "As soon as it left the club, I knew it was going to be pretty good.

"It was an unbelievable buzz. You've got a few thousand people on the left-hand side so it was a special moment and the hairs on the back of your neck were standing up."

Among the other big names, twice Masters champion Phil Mickelson and twice U.S. Open winner Retief Goosen opened with 71s. Fiji's Vijay Singh, the 2000 champion, carded a 72 while Ireland's Padraig Harrington, winner of last year's British Open, opened with a 74.

(Editing by Greg Stutchbury)