SAN DIEGO – The last two years, Kazuo Matsui had homered in his first at-bat of the year.

Now he’s done it three straight.

The Mets’ second baseman had been out all season with a right knee MCL sprain, and in last night’s 7-2 Met win, he made his season debut. Hitting eighth, Matsui led off the top of the third inning against San Diego’s Jake Peavy and lined an inside-the-park homer.

“It’s hard for me because I’m having difficulties trying to get a grasp of it as well, especially the third one this year today, it was an inside-the-parker,” Matsui said. “I can’t even believe it myself.”

It’s a stunning achievement for Matsui – the last player to homer in his first at-bat three straight years was Ken Griffey Jr. from 1997-99, according to the Elias Sports Bureau.

“I feel sorry being compared to him,” Matsui said. “It’s Ken Griffey.”

On a 2-1 pitch last night, Matsui lined the ball into right field, and San Diego’s Brian Giles had it hit off his glove.

But Matsui didn’t know then that he had a homer.

“No, I thought it was a triple,” he said. “Manny [Acta, third-base coach] was just waving me in.”

Matsui kept running, sliding into home plate, the Mets’ first inside-the-park homer since Marlon Anderson last June.

In 2004, in Matsui’s first at-bat of the season, he homered off then-Atlanta pitcher Russ Ortiz on the first pitch of the year. Then last year, he went deep in his first at-bat of the season against Cincinnati’s Paul Wilson.

With Anderson Hernandez on the DL with a bulging disc, Matsui got the start last night. He said in pregame there were “no problems” with his knee. But being back is another chance for him to prove he can be a regular player.

“I feel this is an opportunity but obviously we want to bring the team in first,” he said before the game. “I’m just going to do whatever I can to help us get the W.”