(Adds Woods quotes, details)

ORLANDO, Florida, March 25 (Reuters) - Tiger Woods ended his

two and a half year drought on the PGA Tour when he won the

Arnold Palmer Invitational by five strokes on Sunday, sending a

warning signal to his rivals ahead of next month's Masters.

The former world number one shot a final round 70 to finish

at 13-under-par at the Bay Hill course where had won six times

before.

The American claimed his 72nd PGA Tour title and his first

since the BMW Championship in Sept. 2009.

"It does feel good. It feels really good. It has been a lot

of hard work," Woods said.

"I am so thankful for a lot of people helping me along the

way, they know who they are."

Northern Ireland's Graeme McDowell, the 2010 U.S. Open

champion, finished second, five shots behind Woods, after

starting the final round a shot in arrears.

The win was the first for Woods since the very public

breakdown of his marriage after sordid details of his affairs

were revealed.

It was also the first victory for Woods since the rebuilding

of his swing by coach Sean Foley and comes just two weeks after

he limped out of a PGA event at Doral, raising doubts about his

fitness for the Masters.

McDowell was never able to mount a serious challenge to

Woods after he made a double bogey on the first hole, going from

one greenside bunker to another and closed with a 74.

Woods led by four at the turn and maintained his composure

on the back nine in a time to end his title drought and boost

his confidence ahead of the Masters.

Fast greens and high winds made for some challenging

conditions but Woods limited himself to two bogeys and made some

key saves, including a 13-foot putt for par on the 15th that

effectively ended McDowell's hopes.

Fans followed Woods down to the 18th green, cheering wildly

and after he made par on the final hole, the old chant of

"Tiger, Tiger" boomed out from the gallery.

"It was incredible to have that type of support here," said

Woods.

"I used to live here for a long time, it was neat to see

some of my friends come out and follow and it was just great

atmosphere around all week."

Woods has already 14 majors but none since the 2008 U.S.

Open and will be among the favourites to challenge at Augusta,

along with the world's top two Luke Donald and Rory McIlroy.

"I'm excited there is no doubt. I am looking forward for the

momentum that I've built here and the things that I have worked

on in my game all coming together at the right time," he said.

(Editing by Julian Linden)