Padraig Harrington charged into the early clubhouse lead with a superb six-under-par 65, his low round of the year so far, in the second round of the Transitions Championship in Florida.
Four behind after his opening 69, the three-time major winner gave his best iron display for some time to reach halfway on eight under, one ahead of American Jim Furyk and Swede Carl Pettersson.
Harrington, without a Tour win since he won back-to-back majors at The Open and US PGA two years ago, grabbed seven birdies and would have led on his own but for a bogey at the demanding sixth hole.
Starting on the back nine the Dubliner, back at the Innisbrook course at Palm Harbor after a St Patrick's Day dinner hosted by President Obama at the White House on Wednesday, pitched to two feet on the 11th and then struck a 185-yard approach to four feet at the 16th.
He then had to hole from only 20 inches, eight feet and 10 feet on the first, third and fifth greens and after his only dropped shot at the next he found the target from eight and 10 feet again at the seventh and ninth.
Harrington, joint third in the WGC-CA Championship in Miami on Sunday, was level at that point, but in the group behind him Furyk bunkered his drive down the ninth and bogeyed to match Pettersson's bogey-free 68.
Harrington said afterwards that his relative lack of knowledge about the course had worked in his favour.
"Because I don't know so many of the shots I have to keep hitting at the flags and it seems to be working quite nicely," he said.
"The greens are superb and the wind was predictable, so it was a good morning for scoring.
"I'm capable of winning in the form I'm in. Am I in my best form? No. Am I getting there? Yes.
"You put yourself out there and you put yourself at the line. That tests where your game is at. Some weeks the results happen and you get a win and some weeks they won't.
"I've played tournaments where I've played great coming down the stretch and not won and I've played tournaments where I've played average and won."
American Garrett Willis, playing on a sponsor invitation and leader by two overnight, was among the later starters, but a bogey six at the long 11th saw him slip into a tie for fifth on five under.
England's Luke Donald and Ross Fisher both stood three under, Donald after a 68 and Fisher level par for the day with three holes to play.
Compatriots Ian Poulter and Justin Rose were other late starters and looked like having to improve three shots on their opening 73s to survive the halfway cut.
© Press Association