Most of the 45,000 spectators who flocked to the K Club just outside Dublin were there to cheer on their local star, and he beamed with joy at the reception when he walked onto the first tee.
After Harrington and Colin Montgomerie were beaten 1-up by Tiger Woods and Jim Furyk in their morning better-ball match, the Irishman teamed up with countryman Paul McGinley in the afternoon alternate-shot session. Up two holes with three to play, it seemed as if Harrington had rewarded the fans who had waited so long to see him play in the Ryder Cup in his hometown.
But that lead collapsed and the Irish pair wound up with a tie, worth half a point, as Chad Campbell and Zach Johnson birdied the last three holes.
Harrington's wayward play was largely to blame for losing the lead. His tee shot at the 18th, with the Irish pair still 1-up, put McGinley in trouble in the rough alongside a fairway bunker. After McGinley had partially rescued the situation, Harrington launched their third shot so far over the green it almost landed in the water. Although McGinley saved par, the Americans made birdie and squared the match.
Harrington, who had won seven of 12 Ryder Cup matches before Friday, gave credit to the Americans rather than cursing his own play.
'It's disappointing that we didn't win, but I think that Chad and Zach deserved the half,' he said. 'They finished birdie-birdie-birdie, which is what was asked.
'They certainly played good enough golf to get the half. They didn't make any mistakes in the last three holes, and even all the way through the round they played well. I don't begrudge them a half, but I'm a little bit disappointed that we didn't win the match.'
It was all so different two years ago.
Playing with Montgomerie, Harrington won the opening match of Europe's lopsided 18 1/2-9 1/2 victory at Oakland Hills when they beat the top American duo of Woods and Phil Mickelson. He also sank a 30-foot putt to beat Jay Haas in his singles match and finished with four points for the week.
Arriving at the K Club just a few miles from his home, he was expected to be lifted by the hometown support, especially with Woods again in the rival pairing.
Spraying shots into the rough and the water, however, Harrington seemed like a stranger to his local club, and his Irish fans had few chances to cheer their local star. They saw Furyk give the Americans the lead at the first hole with a five-foot birdie putt after Woods had snap-hooked his own tee shot into the lake.
Although Harrington and Montgomerie turned the match their way by going ahead at the seventh, the Americans hit back to move 3-up after a streak of birdies from the eighth.
'Eight to 12 really killed us,' Harrington said. 'We had a lot of chances and (the Americans) happened to hole a lot during those holes. We came out of them 3-down and should have come out 1 or 2-up.'
Montgomerie's birdie 2 at 13 cut the lead to two. But, with holes running out, Harrington pulled his second shot at 15 into the crowd and left the Scot to make sure the Americans didn't go further ahead.
Harrington birdied the par 5, 555-yard 16th to cut the lead to one, but both Europeans missed birdie putts from about 20 feet at 17 and Furyk captured the first point of this Ryder Cup by leaving his first putt to tap-in range.
Because his opening match lasted almost five hours, Harrington only had a few minutes to recover for the afternoon session alongside McGinley and missed a five-foot putt at the first to hand the early lead to Campbell and Johnson.
Harrington rolled in a 20-foot birdie putt at the third to even the match, and the Irish pair then capitalized on some erratic putting by Johnson and Campbell to take a two-hole lead with three to play. But it all went wrong in the closing holes.
McGinley, who holed the winning putt at the 2002 Ryder Cup at the Belfry and also played on the victorious European team at Oakland Hills two years ago, knows how much it meant to the Irish fans to see the event at the K Club.
'I think we're very lucky to be playing a Ryder Cup in Ireland,' he said. 'We had wonderful support from the Irish people. It was just fantastic. What a great thrill to play before your home crowd to have them that passionate as they were today.'
The only thing missing was a hometown victory.