Tiger Woods impressed yet again but Rory McIlroy and Shane Lowry were left to rue final hole mishaps in the Arnold Palmer Invitational at Bay Hill.

Eight-time winner Woods (42) recovered from a double bogey at his 12th hole with three birdies in his last six to post a four-under 68 that leaves him tied for seventh, just four shots behind leader Henrik Stenson in his bid for a ninth win at Bay Hill

It could have been an even better day for McIlroy, who has struggled for over a month, as he played superbly for much of the day until hit a three-wood out of bounds left at the 18th, finishing with a double bogey six for a 69.

"Yeah, and one bad swing at the end," McIlroy said when a reporter complimented him on "17 holes of beautiful golf" before his late mistake denied him his first bogey-free round in the US this year. 

"On The tee shot, I did exactly what I wanted to with the first one, just trying to hit it up the left side and bring it back and just double-crossed it."

It wasn't quite the triple-bogey finish that saw Lowry sign for a costly 75 that leaves him tied for 96th.

But after playing almost flawlessly to share the lead on five-under after 10 holes, McIlroy was drawing on the positives — his improved putting and more consistent ball-striking — rather three missed fairways coming home.

Pleased to see his hard work in practice pay off, he admitted he must play the par-fives as well as Woods, who birdied all four, if he’s to contend this week.

“This is a golf course where you need to play the par-threes well and play the par-fives well and to be only one-under on the par-fives, I need to do that better,” McIlroy said.

"So I guess with shooting what I shot today and only being that, it's not disastrous. But I need to take advantage of the par-fives, because Tiger’s won plenty of times around here and that’s what he did.

“He can be conservative and play conservative for the most part, but if you make birdies on the par-fives, you’re going to be right up there.”

As for his overall play, his missed cut in Tampa last week gave him time to practice and gain more confidence in his putting and long game.

“It was much better than the golf that I’ve been able to produce the last couple weeks,” he said of his opening round.

The Holywood native is tied for 13th with a resurgent Graeme McDowell, five shots behind Sweden’s Henrik Stenson, who made nine birdies and officially used his putter just 20 times in an eight-under 64 to lead by a shot from Web.com Tour graduate Aaron Wise (21) and Oklahoman Talor Gooch (26).

Gooch's immaculate 65 gave him a strokes-gained from tee-to-green tally of 7.646 — a record for Bay Hill since the statistic was first recorded in 2004.

Jimmy Walker, the 2016 US PGA winner, world number seven Rickie Fowler and Bryson DeChambeau are tied for fourth after five-under 67s.

Woods was more than pleased to see his fused back stand up to the chilly early morning conditions, moving quickly three under after seven before a wild drive ended up tangled in a mesh fence and was deemed out of bounds at the 420-yard third, his 12th.

A six there didn’t appear to faze him, however, and he birdied the par-five fourth and sixth, then rolled in a slick, 71-footer from the fringe for a two at the seventh before curling home an 11-footer for par at his final hole.

"I've gotten the feel of playing tournament rounds," said Woods, who admitted that his long birdie putt at the seventh was fortunate to hit the back of the hole rather than career away.

"It was coming over that hill a little too quick. I was just trying to lag it down there, just make my par and get outta here and it had a crash at the hole, which I'm not complaining about, and it went in."

If Woods and McIlroy showed signs that they’re finding form for the Masters, world No 215 McDowell knows he needs to win soon if he’s to make a tenth appearance at Augusta National next month.

Despite the disappointment of closing with a 77 in the Genesis Open at Riviera Country Club last month when he was just two shots behind eventual winner Bubba Watson going out, the Portrush man was pleased at least to contend that week.

Confident a watershed week is not far away, he made two birdies and an eagle three at the 16th, his seventh, and dropped just one shot thanks to some accurate play from the tee and strong iron play.

“The game continues to be trending in the right direction,” McDowell said. "I feel like mentally I'm starting to gear into where I need to be and it's just a case of really being patient. 

"It's rounds like today that I'll really kind of gain that confidence and belief that I need and I just got to keep pouring that back in and someday, somewhere, we'll get it going again."

With two runner-up finishes and four missed cuts in ten starts at what amounts to a home venue for him, McDowell is hoping to build on his solid start.

"My history around here's a little rugged — I've had a lot of missed cuts, but I had a couple of seconds and couple of top-10s — and I do like this golf course," he said.

After missing four of his first five cuts this year, Pádraig Harrington bogeyed the last for an otherwise encouraging 71 that leaves him tied for 32nd at a venue where he tied for 11th, six shots behind Woods in 2009.

But the 18th proved more costly for Lowry, whose game has also been trending upwards in recent weeks for little reward.

After getting back to level par for the day by rolling in a five-footer for eagle at the 16th, he found greenside sand at the 18th and ran through the green with his third, finishing amongst the rocks fronting the water hazard.

He then took three more to get down from the greenside after a penalty drop, signing for a three-over 75.

As for McIlroy, who will complete his Masters warm up in next week's WGC-Dell Technologies Match Play in Austin, he said he worked on "everything" after missing the cut in the Valspar Championship, where Woods tied for second behind Paul Casey.

"I never really like to work on my swing whenever I'm at tournaments because you're trying to just play golf and get the ball where you're looking instead of worrying about how you're doing it," he said after hitting eight of 14 fairways and 10 greens and was sixth for strokes gained on the greens. 

"So it was nice to be able to work on my swing for a couple of days. Messed around a little bit on the putting green and just sort of tried to get a little more instinctive and reactive on the greens. And that's helped a little bit going back to a couple of feels that I've had before."

Back trouble leaves O'Briain on the verge of Sunshine Tour KO

On the Sunshine Tour, Neil O'Briain's hopes of winning the Bobby Locke Trophy awarded to the Rookie of the Year suffered a blow when his hip and back muscles went into spasm on the range before teeing off. 

"Fought as good as I could but looks, bar a miracle, I’ll have to WD tomorrow," O'Briain said after a seven-over 79 at Serengeti Golf & Wildlife Estate left him second last in the 42-strong field. 

"Absolutely gutted."

O'Briain has a (Rand) R14,372 lead over rival Zack Byrd but the American is 23rd after a 73 and a top 20 finish could be enough for him if O'Briain withdraws.