Credit: John Shearer/Getty; Felix Foto / Splash News

Maria has mad love for Yeezy!

Maria Shriver was a surprise celeb guest at Saturday's Call of Duty XP launch bash held inside a hangar in Playa del Ray, Calif. -- where Kanye West put on a rousing show.

The single mom, journalist and former First Lady of California (in the midst of divorcing Arnold Schwarzenegger) slipped into the show last minute with a group of female friends and Christopher, her 13 year-old son who has recovered from a scary surfing accident mid-summer.

As West blazed through his set, Shriver, 55, sang along happily -- and knew all the words to "Gold Digger" and most of his other hits, according a witness.

Other celebs on hand for the bash included Dianna Agron, Teri Hatcher, Amber Tamblyn and fiance David Cross, athlete and DWTS contestant Ron Artest . . . and a moody Lindsay Lohan, who refused to pose for photos.