Lastings Milledge was high-fiving fans along the right-field railing, the same way Cal Ripken did 11 years ago on his “victory lap” in Baltimore after breaking Lou Gehrig’s record for consecutive games played.

Ahh, the exuberance of youth. Turns out, the celebration was premature – and it irked a few folks in both dugouts.

Pedro Feliz hit an RBI single in the 12th inning and the San Francisco Giants finally held off the Mets 7-6 yesterday, overcoming a breakout performance by the Mets’ prized prospect.

With the Mets down to their final strike in the 10th, Milledge hit his first career homer off All-Star closer Armando Benitez to tie it at 6. The 21-year-old rookie raised his index finger toward the sky as he rounded first and came out for a curtain call.

Then, as he jogged out to right field for the 11th, he slapped hands with dozens of fans leaning over the railing.

“We weren’t too happy about that. But he’s a young kid,” Giants reliever Steve Kline said. “I don’t know if he’s going to be slapping five with everybody after he goes 0-for-15 and the New York fans are booing him.”

The Mets also took notice.

“Oh, boy. He has a little growing up to do,” Cliff Floyd said. “I’ll just mention to him the consequences that come along with that. If that’s what you want to do, you do that. But at the same time, if you want guys throwing at your head constantly, you proceed to do it that way.”

Milledge heard it from his manager, too.

“I had a little conversation with him about that. I told him to tone it down a little bit,” Willie Randolph said. “He got excited about his first big home run. Wouldn’t you? I talked to him about it – it won’t happen again.”

Milledge also hit a go-ahead double and made a sliding catch in right field in his fifth major league game, quickly winning over Mets fans.

“Now I know what’s expected. It was a rookie mistake. We learn from it,” Milledge said. “I was just excited to get the team back. If it was just a solo homer that meant nothing for the team, I wouldn’t have been that excited.”

Steve Finley had three hits and a key sacrifice for the Giants, who took two of three in a back-and-forth series. The teams split six meetings this season – with three going to extra innings.

David Wright hit two homers, including a tying shot in the eighth, and Steve Trachsel allowed one run on six hits in seven strong innings for the Mets, who won their previous four series.

The Giants went up 6-4 in the 10th when Ray Durham and Eliezer Alfonzo hit two-out, two-strike RBI singles against Aaron Heilman. But the Mets, who have fought back from late deficits all season, weren’t done. Jose Valentin homered with one out in the bottom half off Benitez, who had dominated his former team since being traded in July 2003.With two outs, Milledge drove a 1-2 pitch over the left-field fence.

The score stayed tied until the 12th, when Lance Niekro led off with a single and pitcher Pedro Feliciano threw wide to second on Jason Ellison’s bunt for an error. Finley advanced the runners with a sacrifice bunt and Feliz singled off Heath Bell.