The Ireland captain knocked home his 22nd goal of the season in the dying stages of their 3-1 final win over Houston Dynamo, converting a penalty with trademark confidence.
Beckham's goodbye was the story of the day, but Keane's resurgence in the second half of the campaign has been at the heart of their charge to glory.
Now, the big question is if the 32-year-old will return to the Premier League for another cameo this winter. It would be hard for his employers to stand in the way after his contribution to their success.
LA's main mission between now and 2013 is to find the star quality to replace Beckham, with Kaka at the top of the shopping list, ahead of Frank Lampard. The departing star may end up having a significant say, with discussions under way to ensure that his last match with Galaxy was not a Hollywood ending.
Last week, it emerged that negotiations are taking place between Beckham and Galaxy that are set to see him buy a 25pc stake in the franchise. He has an option to purchase an expansion club at a knock-down rate, but that excludes New York, the league's next target.
MLS and AEG, the Galaxy owners, would prefer to keep the Beckham bandwagon rolling. Even if based abroad in the coming year, he could still act as an ambassador and recruiter for Galaxy.
AEG president Tim Leiweke said Beckham is trying to persuade Kaka to leave Madrid. "David has done the yeoman's work on our behalf at introducing us, getting him comfortable, getting his family comfortable, talking about LA and the organisation," Leiweke said.
As for the football: where next for Beckham? The firmest interest has come from Australia, though the player still believes he is good enough to feature for a Champions League club, and his wife, Victoria, was reportedly house-hunting in London last week. The only certainty is his desire to continue playing for as long as his body will allow.
Houston threatened to spoil the party by taking the lead through Calen Carr shortly before half-time, but an Omar Gonzalez header and penalties from Landon Donovan and Keane ensured the scoreline reflected Galaxy's superiority.
It briefly looked as if Beckham would take the late penalty that made the score 3-1, but Keane grabbed the ball and took control on a night where he had two goals chalked off by the officials.
Beckham and Donovan were in discussion before Keane converted, leading some to believe that the Englishman wanted the perfect send-off.
"I told Landon to take it but he told me he was too tired, so we should let Robbie have it," Beckham explained. "I wanted to win the game. It is not about me scoring a penalty to top things off. It's about winning the game and winning the championship."
With Donovan's future also up in the air, Keane could be the senior figure in the 2013 dressing-room, with the popularity to match. It took longer for Beckham to win the Californians over. Three years ago, he was heckled and his commitment to MLS was questioned after a loan spell with AC Milan.
But as at Manchester United and Real Madrid, he signed off on a winning note.