AUGUSTA - Sweden's Carl Pettersson set the early pace as the 77th Masters got underway Thursday with all eyes on Tiger Woods as he looked to seal a remarkable return to the top with another major title.

The burly Pettersson, playing in his fifth Masters, birdied Augusta National's opening two holes to take the lead at two under with American Brian Gay joining him on that mark after a birdie at the par-three sixth. Woods meanwhile was warming up on the practice green ahead of a mid-morning start which could prove to be providential given the forecast for stormy weather later in the afternoon.

The 37-year-old American has regained the world number one spot from Rory McIlroy after three wins in the four stroke-play events he has played this year. He says he is fit and healthy and is enjoying what he calls true "balance" in his life. That combination of factors he has not enjoyed for the last few years and he is optimistic they will renew his march on golfing history with a 15th major title, nearly five years after his last win.

That would leave him just three majors short of achieving his life-long ambition of matching and eventually surpassing Jack Nicklaus' record of 18 major titles, the last of which came here in 1986 at the age of 46. Asked whether he would trade his newly-regained number one spot for another major, Woods left no doubt, saying: "Oh absolutely. Are you kidding me?"

A win on Sunday would also make it five Green Jackets for Woods -- his last was in 2005 -- just one behind the record six held by Nicklaus. Two other stories have dominated the buildup to the opening round -- has Rory McIlroy finally got to grips with his new clubs and secondly how will 14-year-old Chinese prodigy Guan Tianlang fare on his Masters debut.

McIlroy finally showed a clear sign that he is emerging from his four-month slump with a closing 66 for second place at the Texas Open last week, but it remains to be seen whether he can safely negotiate four rounds over a course that has hurt him badly before. He has already set his sights high, saying that anything less than a win on Sunday would be a disappointment in what he says is his favorite tournament of the year.

The Ulsterman, who celebrates his 24th birthday next month, already has two major title wins to his credit -- both by eight strokes -- at the 2011 US Open and at last year's PGA Championship. A win at Augusta National would leave him needing only a British Open title to complete the full set of majors.

Astonishingly, McIlroy, one of the youngest players in the 93-strong field, is 10 years older than Guan, who will become the youngest player in Masters history when he sets off on Thursday. Short off the tee, the slightly built Chinese boy is expected to struggle over the mighty 7,435-yard Georgia layout and it remains to be seen whether his superb short game can bail him out.

Of the 19 past champions playing, three-time winner Phil Mickelson looks the best bet after Woods, although he admits to feeling oddly nervous having broken with custom to stay idle the week before the tournament. McIlroy apart, the quest to be the first European winner since Jose Maria Olazabal in 1999 continues with former world number ones Luke Donald, Lee Westwood and Martin Kaymer all looking for success.

Many feel though that world number three Justin Rose could be the best bet from Europe as he has a genuine liking and feeling for the particular demands of Augusta National.