Shane Lowry was the strongest Irish performer on a day when Tiger Woods showed flashes of his brilliant best in the Valspar Championship.

Lowry's even par round of 71 left him the best placed of the five-strong Irish field after the opening day's play at the Copperhead course at Innisbrook. 

The Offaly golfer started his round on the back nine and birdied the 11th (his second hole) and remained at one under at the turn. 

However, he bogeyed two of his first three holes on the way in and required a birdie on the seventh to return him to even par by the end of the day's play. 

He is currently four back from the lead held by Canada's Corey Conners. 

By contrast, Rory McIlroy's Masters preparations suffered another blow as he finished Thursday on three over par.

McIlroy's only birdie in an opening 74 came courtesy of holing a bunker shot on the seventh, his 16th hole of the day, while two bogeys and a clumsy double-bogey seven on the fifth left him three over par.

He is one shot further back from his compatriot Graeme McDowell who struck a two over par 73. 

And it was a more difficult day still for the remaining Irish contenders, Padraig Harrington and Seamus Power, who find themselves at five over par after grim opening rounds of 76. Both will need to shoot low numbers to have a chance of sticking around for the weekend. 

Three shots off the lead is Woods, whose action-packed 70 featured a vintage - and highly risky - escape from trouble on the 16th.

Playing in his fourth PGA Tour event since undergoing spinal fusion surgery last April, Woods was just two shots off the pace after three birdies in four holes around the turn, before dropping shots on the 12th and 13th.

Another bogey looked on the cards after Woods pulled his tee shot on the 16th into the trees, but the 14-time major winner conjured a hooked approach to just short of the green despite slamming his club and left arm into the trunk of a tree on his follow-through.

Woods appeared to be wincing in pain as he walked up the fairway but chipped close to save par and then produced the shot of the day on the par-three 17th to set up a tap-in birdie.

Woods told NBC: "It was really brutal out there. We as a group got fooled a lot today [by the wind]. It was tough. Today was a very good test and I felt like I really controlled the ball well for most of the day. I'm revved up. I love competing, I love mixing it up with these guys. "

Asked about his second shot on the 16th, Woods added: "If I went over that sign in the water and I turned it, I'd be all right. The problem is I'd have to put a little speed into it and I was going to feel it.

"It didn't feel very good. I moved all the people and warned them in case that club breaks."

McIlroy is at three over par after his opening round in Florida

McIlroy began the season in superb form with a tie for third in Abu Dhabi and a runners-up finish in Dubai, but missed the cut on his first PGA Tour start at Pebble Beach and followed that with a tie for 20th in the Genesis Open and 59th in the Honda Classic.

McIlroy told a pre-tournament press conference at Innisbrook that he was "totally ready" for the Masters and felt he would have a good chance of the victory he needs at Augusta National to complete the career grand slam if the first major of the year got under way this week.

But his performance on Thursday told a somewhat different story after starting from the 10th with 10 straight pars before failing to get up and down from a greenside bunker on the second.

Worse was to come on the fifth after a wayward drive into the trees forced McIlroy to pitch out sideways, a mistake he compounded by taking four to get down from just short of the green.

And although the birdie on the seventh repaired some of the damage, McIlroy dropped another shot on his final hole to card a fifth consecutive over-par round on the PGA for the first time since April 2010.

Scotland's Russell Knox was two shots off the lead after an opening 69, with Masters champion Sergio Garcia, Justin Rose, Luke Donald and Paul Casey all alongside Woods on one under.