Making his 24th consecutive appearance in the event, Harrington recorded eight birdies and a solitary bogey to establish a new course record of 63 - enough to give him a one-shot lead over late-starting South African Zander Lombard at the top of a crowded leaderboard.
Eddie Pepperell marked his return from a seven-week injury lay-off with a 65 to share third place with compatriot Lee Slattery, Thorbjorn Olesen, Wade Ormsby, Mike Lorenzo-Vera and Hyowon Park, with Bob MacIntyre, Lee Westwood, Shane Lowry, Martin Kaymer and Ian Poulter part of a large group on four under.
A broken wrist at the end of last year kept Harrington out of action until March and the three-time major champion started the week ranked 291st in the world after missing the cut in three of his last four events. “Every week feels like my first week out, trying to find my game, but links golf suits me because you can really work your way around,” said the 47-year-old Ryder Cup captain, who shot rounds of 68-78 last year at Ballyliffin to miss the cut.
“I had neutral expectations. I just wanted to take stock of my game and did not expect a 63 but it was a bit of a stroll in the park. I’ve worked a lot harder to shoot 73, that’s for sure.
“It was buzzing out there and it would only be bettered if I did it on Sunday, but if you don’t do something on Thursday you won’t be around for Sunday anyway. All this does is create a number of scenarios where I can go on and win.”
Lorenzo-Vera had earlier shrugged off the embarrassment of suffering a dreaded shank to post a five-under-par 65 as he chases a first European Tour title in the £5.5million event. “I am a little bit ashamed of this one but I shanked one on 11, the par 3, like proper shank into huge rough,” he admitted. “I didn’t shank a golf shot for five or six years in a tournament, so that was a bit strange. After those kinds of shots you laugh, and I was just trying to make a good bogey there, hit it to around 15 metres and got the bonus to hole the putt. I just went to the next tee with a big smile and bombed one down the middle and birdied the next two holes, so that was a big turning point.”
MacIntyre, one of five Scots currently exempt for the Open Championship, carded six birdies, including the last, in his latest eye-catching display, which left him a shot ahead of compatriot and defending champion Russell Knox.
“I didn’t play my best golf,” admitted MacIntyre, pictured. “Off the tee, I was really bad, but I managed to get the breaks and my short game was sharp, which makes it easier. Though I might not have needed them, I put different clubs into the bag this week just to prepare myself for The Open, which is the big one.”
Knox, who has finished first and second in his two appearances in this event, opened with a bogey-free effort but said: “It was a full grind today. I didn’t feel like I played amazing. I scored probably as good as I should have. My short game was good and when I did get off line I got it back in play and recovered. I’m pretty thrilled with three-under.”
David Law and Liam Johnston were next best among the Scots with 68s while Richie Ramsay also broke par with a 69. David Drysdale had a 70, one better than Stephen Gallacher and Grant Forrest, with Scott Jamieson on 73.