The 40-year-old Dubliner is trying to break a hoodoo again this year after winning the curtain-raising par three competition for a record third time.
But the chances of him doing it were certainly improved by a long drive down the 575-yard second and an approach which just carried the front nine and ran about eight feet past the flag.
It was three years ago that it had been a very different story on the hole.
Harrington was Open and USPGA champion then, but his bid for a third successive major victory effectively ended in the third round when he got into all sorts of trouble after a bad drive left into trees and ran up a quadruple bogey.
Despite a slump since then to 96th in the world, his game is clearly not in terrible shape. He began the Transitions Championship in Florida three weeks ago with a career-low 61 and in the par three competition covered the nine holes in a five under par 22.
That was matched by American Jonathan Byrd, but they were declared joint winners when the event was cancelled because of a thunderstorm.
Harrington did follow his eagle with a bogey at the difficult short fourth, however, and so was only sharing top spot with American trio Stewart Cink, Rickie Fowler and Kyle Stanley, Australian Aaron Baddeley and Japanese amateur Hideki Matsuyama, the only player in the first 33 to start with a birdie.
The action began at 7.40am local time with Gary Player joining Jack Nicklaus and Arnold Palmer as honorary starters - and showing them what he is still capable of.
The 76-year-old South African followed 82-year-old Palmer onto the tee for a ceremonial opening drive and found the middle of the fairway some 250 yards away.
It was around 50 yards further than Palmer and 72-year-old Nicklaus then split the difference between them.
With that the trio, who used to be known as golf's "Big Three" - they have 13 Masters titles between them - retired to the clubhouse and allowed the tournament proper to begin.
Conditions were perfect for the early starters. Torrential rain on Tuesday night had softened up Augusta National and it was a bright, still morning as the 76th Masters began.
Scotland's Paul Lawrie, back in the event for the first time since 2004, followed seven opening pars with a bogey at the long eighth, while England's Ross Fisher had bogey fours on the fourth and sixth.
Compatriot Justin Rose, winner of the season's second world championships last month, set off with two regulation pars as many of the crowd waited for four-time winner Tiger Woods to begin his challenge.
He was being followed by world number one Luke Donald, but Rory McIlroy, whose runaway US Open victory last June came two months after he blew The Masters with a closing 80, was out in the penultimate group of the day at 1.42pm local time.
Woods, winner on his last start, single-putted the first three holes, but only the last of them was for birdie.
His hooked drive hit a tree off the opening tee, but he saved par from eight feet and then made a six-footer for par on the next after again going left and this time taking a penalty drop.
At the 350-yard third, his pitch finished just under 10 feet from the flag and he converted that to move into a large group on one under.
New leader on three under was Swede Henrik Stenson, who matched Harrington's eagle and then birdied the fifth, while second on his own was German Martin Kaymer.
The former world number one has yet to make the cut on the course, but after an opening bogey he reached the turn in 34 and remained two under with seven to play.
Harrington started for home one under and Lawrie joined him, Woods and a whole host of others by making eagle at the long 13th.
Donald bogeyed the first after pushing his drive into the trees, but two-putted the next to return to level par alongside Rose, who parred the first seven.
Fisher birdied seven and eight, but a four at the short 12th put him one over again.
The field was reduced to 95 when 1998 winner Mark O'Meara followed Dustin Johnson in withdrawing because of injury.
That left Scot Martin Laird playing in a two-ball with American Chez Reavie. He parred the first two holes, but compatriot Sandy Lyle, the 1988 champion, followed an opening bogey with a seven at the second after hooking deep into the trees.
Lawrie had never managed an eagle in 14 previous rounds at Augusta, but when he made it two in three holes on the 530-yard 15th he joined Stenson in the lead at three under.
The 43-year-old had never broken 70 before either, but three closing pars would give him a 69 and he achieved the first of them after narrowly avoiding the bunker at the short 16th.