A last-hole bogey failed to take the gloss off a superb performance from Tiger Woods as the former world number one continued to impress on the latest leg of his improbable comeback in the Valspar Championship.

His three under par round of 68 takes him to four under for the championship and a share of the lead with Paul Casey, Brandt Snedeker and Casey Conners, the last of whom is in the early stages of his second round. 

Shane Lowry is in the clubhouse as the best performing Irish player after a one under par round of 70 leaves him three strokes off the lead. 

The Offaly man got off to a sluggish start and was two over par for the championship thru seven but he pulled one back on the 8th before adding two more birdies on the back nine to leave him under par for the championship. 

Woods showed flashes of his brilliant best in an opening 70 in what is just his fourth PGA Tour event since undergoing spinal fusion surgery - his fourth back operation in three years - last April.

And the 14-time major winner surged to the top of the leaderboard for the first time since August 2015 before having to settle for a share of the clubhouse lead with England's Paul Casey and Brandt Snedeker.

Starting on the back nine of the testing Copperhead Course at Innisbrook Resort, Woods recovered from a wayward drive on the 10th to make par and also parred the next before holing from five feet for birdie on the 12th.

A superb approach to the 13th set up another birdie from a similar distance and, after a run of six straight pars, another gain on the second took Woods into a share of the lead.

Woods enjoyed a stroke of good fortune on the par-five fifth when his hooked drive appeared to hit a cart path and bounce back on to the fairway.

And the 42-year-old took full advantage by finding a greenside bunker with his approach, splashing out to four feet and holing the birdie putt to take the outright lead.

The last time that happened was during the third round of the Wyndham Championship in August 2015 and the last time Woods led outright after a PGA Tour round was after his last win in the 2013 WGC-Bridgestone.

The prospects of the outright lead disappeared with a bogey on the ninth when he pushed his approach right of the green and it finished up in a female spectator's handbag.

After taking a free drop, Woods caught the pin with his chip but was unable to hole from six feet for par, leaving him to sign for a 68 and share of the lead on four under par.

"I'm up there," Woods told PGA Tour Live. "I don't think this will be leading [at the end of the day] but at least I'm there with a chance going into the weekend.

"Today was a good day. It was cold early, then the wind started blowing a little bit - it was inconsistent and tough to get a bead on. Did a lot of guessing and guessed pretty good, also got fooled a few times.

"I keep getting a little bit better here and there, making these little subtle tweaks. I've done that from tournament to tournament, I just need to get a little bit more tournament time in and I think I've done that.

"I'm starting to get a better feel for it, I'm finding the rhythm of the rounds, I'm hitting shots, I don't have a problem posting scores. I'm able to play more feel golf than just trying to figure out how to play golf again."

Playing partners Jordan Spieth and Henrik Stenson, the last two Open champions, were set to miss the cut after finishing five and six over respectively. 

While Shane Lowry is in a promising position after Friday, Padraig Harrington endured another tough day, hitting a two over par 73 which leaves him at seven over par for the championship.