MARBELLA, Spain (Reuters) - Holder Lee Westwood made a blistering start in Thursday's Andalucia Open first round with a flawless seven-under-par 65 securing an early one-stroke lead.

Westwood's excellent opening was almost overshadowed though by 20-year-old Danny Willett.

The European Tour debutant, ranked the world's top amateur by the Royal and Ancient Golf Club, could have shared the lead with his fellow Briton but for a bogey at his final hole.

Two eagles helped Willett tie for second place on 66 with Norwegian Jan-Are Larsen.

Westwood reeled off seven birdies as he improved on his opening round of 2007 by seven strokes.

The 2000 European number one, riding high in third spot on this year's order of merit, is pleased his game is in good shape with the U.S. Masters looming in two weeks' time.

Westwood told a news conference he had taken every step to ensure it was, including going through a video putting session with his father and coach John on Tuesday.

"I'm playing with a lot of freedom at the moment and a 65 shows I've got a lot of confidence," said the Ryder Cup stalwart.

"I used a similar game-plan to last year but my game's always a work in progress. I've got a few things I'm working on with one eye on the Masters."

SPANISH TITLE

Willett's recent Spanish Amateur title impressed the tournament sponsors enough to hand out an invitation to the youngster and he took immediate advantage by eagling his first hole.

"I was quite nervous for my first European Tour event," said the Englishman. "There was quite a bit of pressure to try to play well because of the invitation.

"The eagle took a lot of first-hole nerves away and relieved the pressure. I just enjoyed myself then."

Willett is planning to try for his professional card at the end of the year but said he would leave the amateur ranks instantly, like Spain's Pablo Martin did after his victory at last year's Portuguese Open, if he won on Sunday.

"I'd have 14 days to decide but the thought of the (tour) exemption would be too much of a temptation," said Willett.

Twice former U.S. Masters champion Jose Maria Olazabal, returning after seven months out with injury, began promisingly with an opening birdie and had not dropped a shot through six holes.

(Editing by Tony Jimenez)