Beckham won his first MLS championship in the final game of his groundbreaking five-year contract with the Galaxy, who rolled through the postseason to the franchise’s third league title after finishing with the league’s best regular-season record.

“I’ve wanted to be successful for the Galaxy for five years, and tonight, I have that,’’ Beckham said.

Beckham punctuated a solid performance in the MLS Cup with an alert header to Keane, the Irish striker who joined Los Angeles in midseason. Keane made a run and eventually fed Donovan, who struck home his record 20th MLS playoff goal.

“To be honest, the actual goal doesn’t mean a lot to me,’’ said Donovan, selected the MLS Cup MVP. “For the last two months, we’ve just been so determined. I didn’t care if it was an own-goal that won it. Winning feels so good.’’

Beckham lifted Donovan off his feet with a hug after the final whistle in the Galaxy’s record seventh appearance in the league title game.

“It’s been the most enjoyable time of my career in America over the last year, and this just tops it off,’’ said Beckham, whose services are coveted by Paris Saint-Germain and a handful of British clubs. “I’ve said before, I need to sit back and relax and enjoy this moment, and then I’ll figure out what I’m going to do next year. I might talk in the past tense sometimes, but that doesn’t mean I’m not coming back.’’

Beckham planned to celebrate through the night - but only until dawn.

“I’ve got school drop-off at 8 o’clock,’’ he said, laughing.

Los Angeles had the most expensive and highest-profile roster in MLS history, but the Galaxy got full value from their three highest-priced players, particularly in the playoffs. Beckham’s assist was his fourth of a stellar postseason, while Donovan scored in each of the Galaxy’s final three playoff games, and Keane was a serious offensive force despite flying across the world in his spare time on Irish national team duty.

A sellout crowd of 30,281 at Home Depot Center - where the Galaxy didn’t lose a game all season long - cheered Los Angeles past the Dynamo, who hadn’t lost in nine games since Sept. 10. Houston struggled for offense in the MLS Cup after losing leading scorer and league MVP runner-up Brad Davis to a torn quadriceps in the Eastern Conference championship.

Beckham put a stylish finish on the best season of his five-year stint with the Galaxy, finishing second in MLS with 15 assists while spending the entire season in Los Angeles.

The Galaxy dominated play in the scoreless first half, with the cautious Dynamo sitting back while Los Angeles pressed. Beckham was the most creative attacker, but the Galaxy struggled to finish his service - nobody more than forward Adam Cristman.

Beckham put a perfect corner kick onto Cristman’s head in the 12th minute, but the Los Angeles forward botched the finish. He then missed back-to-back chances starting in the 27th minute, failing to convert another header on Beckham’s pass over the defense before losing his footing and misplaying a ball from Donovan inside the penalty area moments later.

After Keane barely missed a shot across the mouth of the goal early in the second half, he slipped a shot between goalkeeper Tally Hall’s legs in the 56th minute, but was whistled offside by the smallest of margins.

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MLS will have 10 playoff teams and more games between regional rivals under new competition policies in 2012.

Next year’s MLS Cup will be hosted by the finalist with the most regular-season points, a change from the league’s tradition of neutral-site championship games.

After a regular season weighted for games within each conference, five teams will make the postseason from each conference. The bottom two seeds will play a knockout game to determine who takes on each conference’s top seed in a two-game aggregate-goal format. The conference finals also will be played in a two-game series.