Harrington was the first man to break 69 at Augusta this week

Harrington, who opened with a 77, began with three straight birdies but tripped up with a double at the seventh before staging an impressive finish.

He joined England's David Howell (75) and in-form Welsh debutant Bradley Dredge, who shot 70.

Paul Casey was also a man on a mission, adding a 68 to his opening 79 to reach three over with Luke Donald (74).

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Sweden's Henrik Stenson, the world number six, had an adventurous round and came home in 42, including a double bogey on the 18th, to end on 76, four over for the tournament.

Harrington, whose best Masters finish was tied fifth in 2002, bounced back from his double bogey with four birdies to finish, marred by just one bogey on 10.

"I thought the course was an excellent test and set up very well," he said. "It was a good mental test - when to go for pins and when to play safe.

"You've got to give it your full attention. Yesterday I messed up a lot of simple shots."

Howell, 31, began with a double-bogey after taking two to get out of a greenside bunker. He dropped another shot on the second after an errant drive, but steadied the ship with a birdie at the eighth.

Three over isn't what you want but the way I hit the ball, beggars can't be choosers David Howell

He picked up another shot on 10 but bogeys on 11 and 18, via another wayward tee shot, pegged him back.

"An interesting day," said Howell, who was in contention on his debut two years ago before running into a red-hot Tiger Woods.

"I'm not in control of the ball as I would like to be - I haven't been all year - but I'm not going to be a million miles away at the end of the day.

"I'm in the hunt again at Augusta, which is wonderful.

"I dodged a bullet on the 18th. It could easily have been a six or a seven.

"Three over is not what you want on the Friday of a major, but the way I hit the ball beggars can't be choosers."

Dredge birdied 17 but handed the shot back on 18 to miss out on a 69 after beginning with two straight birdies.

"I'm pretty excited to be in the mix and the 17th was a massive bonus," said the 33-year-old. "I didn't hit the ball great, but I hit some good shots when it mattered. You've just got to grind it out here and put the blinkers on."

Casey's round included an eagle with a monster putt at the long second and a stunning birdie on the par-three 16th in which his ball was inches from a hole-in-one.

"I feel like I'm in contention. I'm not that far back and if I carry on like that I might have an outside chance," he said.