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.”
Meanwhile Irish golfing sensation Rory Mcllroy yesterday said the University of Ulster’s model of combining sport with education is the way forward for producing world-class home-grown athletes.
The Co Down golfer was speaking as he officially opened the University of Ulster’s Sport and Exercise Sciences Research Institute (SESRI) laboratories, at the Jordanstown campus.
McIlroy unveiled a plaque at the £1.275million facilities, before showing off his skills at the state-of-the-art scientific analysis suite, smashing some 300-yard plus drives down the virtual golfing fairway.
When asked if the academic and sport-linked model, like the one operating at Ulster, was the best way forward for sport, he said: “It is, yes definitely.
“In terms of all sports, the University of Ulster has everything you need here. Facilities outdoors where you can practice your sport, whether it be football, hockey, rugby or whatever else and then the facilities inside to become stronger, more agile, more flexible — there are all the resources here that you need.”
The machine — which is the first of its kind to be used in Ireland and one of only three in Britain — can measure free radicals in the body, which can determine the likelihood of long-term development of chronic disease.