Harrington won his maiden major at the Open last July
Open champion Padraig Harrington cut a frustrated figure after carding a two-over 74 in the first round of the Masters at Augusta.
The Dubliner was level par with three holes left before bogeys at 16 and 18 spoiled his card.
"Bogeying the last made it a pretty disappointing day," said Harrington.
"I missed a lot of chances. I struggled off the tee and struggled putting, probably the two most important things on this golf course."
Harrington is six shots off the lead shared by England's Justin Rose and South African Trevor Immelman who are at four under after rounds of 68.
Brian Bateman, Brandt Snedeker and England's Lee Westwood are one shot back at three-under.
Harrington, who beat Sergio Garcia in a play-off to win the Open at Carnoustie last year, birdied the 2nd but made a double-bogey six on the 5th before another birdie on 13.
But the 36-year-old said he was not struggling to live up to his billing as a major champion.
"There's certainly more pressure from outside," he said. "But I'll just do my own thing and see what happens. There's still a long way to go."
England's Nick Dougherty also carded 74 on his Masters debut, as did South African Ernie Els and fancied Swede Henrik Stenson.
"Two over is not a bad start, so I'm not too disappointed, but I didn't hit it very good," said Dougherty.
South African Rory Sabbatini, who won the par-three contest, and Australian duo Geoff Ogilvy and Adam Scott all shot 75s alongside former champions Ian Woosnam and Tom Watson.
Someone will come along and break 51 Masters one day, I guess
Two more former winners Jose Maria Olazabal and Fred Couples amassed four-over 76s.
The 48-year-old Couples faces an uphill task to make a record 24th consecutive cut at the Masters.
"I misclubbed a lot of shots, and they were hard shots," said the American, the winner in 1992.
"I didn't hit very good ones and I didn't make many putts. When you do that, it kind of adds up to 76 which is very mediocre."
Garcia also struggled and looks like missing a Masters cut for the third time in four years after claiming five bogeys in an opening 76.
Fellow Spaniard Miguel Angel Jimenez had a birdie at the second but two bogeys on the front nine, and a further four coming home, leaves him on five over.
South African legend Gary Player compiled an 83 as he set a Masters record with his 51st appearance, breaking the record he held with Arnold Palmer.
"Man, that's a tough golf course," said the 72-year-old.
"It's a thrill to know now that I hold the record. Of course all records are made to be broken, aren't they? Somebody will come along and break 51 one day, I guess."