Maria Shriver and Oprah Winfrey Rip Arnold Schwarzenegger During Finale in Chicago's United Center

As Arnold Schwarzenegger's baby drama exploded ... Maria Shriver was in Chicago with Oprah Winfrey for the taping of her farewell show -- and together they took a blatant shot at Arnold ... to the delight of 20,000 fans.

Maria walked on the United Center stage tonight with Oprah's bff Gayle King -- and declared O had always given her "love support, wisdom, and most of all the truth."

Oprah backed that up by emphasizing, "THE TRUTH!" Our spies say everyone in the arena understood it was a message to Arnold -- and the place exploded with applause.

Other guests at the show -- Aretha Franklin, Halle Berry, Simon Cowell, and Jerry Seinfeld ... and Usher closed the show as confetti rained down on the crowd.

Not shockingly, we're told Chi-town hero Michael Jordan got the biggest ovation of any of Oprah's guests.