BOSTON -- Closer Jonathan Papelbon, who never shies away from taking the blame on those rare occasions when he loses a game, didn't need an instant replay to see why he is no longer perfect in save opportunities this season. He knew that he simply made a bad pitch at the wrong time, and that's why the Red Sox fell to the Mets in a 3-2 heartbreaker at Fenway Park on Saturday night.

"It's not shocking, because the simple fact is, it's an overthrown fastball right down the middle," said Papelbon of the two-run homer he surrendered to Omir Santos.

The hit was initially ruled a double but overturned under Major League Baseball's instant replay system -- officially instituted on Aug. 28, 2008 -- which allows the umpires to review questionable home run calls.

As the replay would eventually make the correct call, Papelbon knew that he'd clearly made the wrong pitch.

"The guys in the big leagues, they're going to do that. It just wasn't a well-executed pitch," said Papelbon, who is now 11-for-12 in save opportunities.

With two outs and one on in the top of ninth, Papelbon, clinging to a one-run lead, reached back for a fastball that would finish the Mets. Santos ripped the 97-mph heater over the red line that marks the top of the Green Monster. The ball hit off the ledge just above that line and caromed back into play.

By Fenway Park ground rules, that is a home run. Third-base umpire Paul Nauert said that it hit off the Monster, resulting in a double that set up runners at second and third with two outs.

But after the umpires huddled, they went into tunnel just behind the Boston dugout to initiate the replay. Crew chief Joe West emerged shortly thereafter with the verdict -- a two-run homer.

"Cut and dried," said West. "We looked at the replay, and ... it cleared the red metal piece. [If you] hit the back piece, that is a home run, which is the ground rule here. Looking up in the lights, looking up like he had to, the third-base umpire Paul Nauert made his best effort and felt, in the best interest of the play, to keep it in play, because we can always change it to a home run."

The Red Sox knew that once West opted for the replay, the original call would be overturned.

"From where I'm sitting, it's probably a little anticlimactic," said manager Terry Francona. "I kind of thought I saw what I saw. I was probably hoping against hope, but it's a tough game to lose."

"I thought it was a home run -- I did," said Papelbon. "I saw it go over the line, and I thought I was going to get away with one for a little bit there. Once I saw Joe West walking toward our dugout, I knew that either, A, they were going to go for a replay, or B, they were going to tell [Francona] it was going to be a home run. So I knew it wasn't good from there."

Papelbon's rare misfire spoiled a brilliant night from ace Josh Beckett, who had fired eight innings, allowing five hits and one unearned run.

"I felt good," said Beckett. "I keep making progress."

It was Beckett's fourth quality start in a row, and his best performance since Opening Day.

In actuality, there was something that upset Papelbon even more than the home run pitch.

"I give up a leadoff walk [to Gary Sheffield]," he said. "If I don't do that, maybe we're still playing the ballgame. That's kind of upsetting, because I'm out there overthrowing the ball a little bit. A little too intense for me. I wasn't able to kind of throttle it down."

While Papelbon tried to cool off in the dugout, the Red Sox attempted to rally right back in the bottom of the ninth against J.J. Putz. Kevin Youkilis led off with a walk. Jason Bay hit a rocket to third, but David Wright made a tremendous play and fired to second for the forceout. Mets second baseman Luis Castillo somehow stayed on the bag despite being off-balance. J.D. Drew then hit a laser to right, but it was right at Angel Pagan for the out. Mike Lowell grounded out to end the game.

"We played a good game," said Francona. "We talk so much about maybe trying to spread it out or give yourself a cushion so if you make a mistake, it doesn't cost you a game."

The Boston offense, after getting a two-run single from Youkilis in the bottom of the first, didn't do anything against Mike Pelfrey or the Mets' bullpen for the rest of the night.

Papelbon was left to feel the brunt of the tough loss.

"The way I look at is, I basically pitched two months without blowing a save. I blew a save tonight. I thought the team played great, and I'm going shoulder this one," he said. "This is on my shoulders. It's my job to go out there and preserve the win, and I didn't. It's on me. Tonight's on me. I just want to be back out there and get a chance tomorrow and pick my guys up and let them know that I'm still here kicking."