World No.17 Casey shot a closing six-under-par 65 to finish at 10-under 274 to win by one shot from Woods, who shot a 70, and fellow American Patrick Reed (68) on the Copperhead course at Innisbrook Resort.

The highly-charged Florida event ended with one player ending a long victory drought, just not the one most fans came to see.

The 42-year-old Woods was the centre of attention all Sunday as he chased a first win in almost five years, in just his fourth official event back after undergoing spinal fusion surgery.

The old Tiger magic was missing for most of the day as he struggled with his irons while a cold putter hampered the 14-time major champion.

Missing, that is, until the par-3 17th, where Woods perfectly read and then executed a 44-foot birdie putt, his ball curling deliciously into the centre of the cup as the gallery went berserk.

Woods looks over a putt on the 18th hole at the Valspar Championship that would have forced a playoff against Casey had it fallen. PHOTO: Michael Reaves/Getty Images.

But Woods could not replicate the magic at the par-4 18th, where he missed a difficult 40-foot birdie putt that would have forced a playoff with Casey.

"Today wasn't quite as sharp as I would like to have had it but I had a good chance at winning this tournament," Woods said.

"A couple of putts here and there and it could have been a different story."

Reed blew his chance for a playoff, making an embarrassing bogey at the last when his first putt, through the fringe, failed to make it up the hill and rolled all the way back to his feet.

FINAL LEADERBOARD

For 40-year-old Casey, who had won 17 times around the world, it was only his second US tour victory after the Shell Houston Open in April 2009 and his first win anywhere since the European Tour's 2014 KLM Open.

"The guy (Woods) has got more victories than all of us put together," a relieved Casey said.

"He made it look easy for such a long time and it's not. I won a few times in Europe (13) but to get my second victory on the PGA Tour, it's emotional. I've worked hard for it.

"I lost a friend last Saturday, played with a heavy heart. Maybe that was the difference."

Masters champion Sergio Garcia (65) finished fourth at eight under while 2013 Masters winner Adam Scott (72) was tied-16 at three under.