The get-together Saturday in L.A. served as a two-pronged event ... first, to celebrate O's big day, obviously -- but these ladies also came together to honor Anastasia Beverly Hill's 25th anniversary with a true who's-who guest list.

In addition to the above-mentioned names ... other stars in attendance included Sofia Vergara, Heidi Klum, Lori Harvey, Jessica Alba, Rita Wilson and others. So, yeah -- it was a pretty glitzy affair for the iconic cosmetics store ... and especially Oprah.

Kim snapped photos of O and her elaborate cake ... and Lori got the moment on video. Of course, everyone sang 'Happy Birthday' at the top of their lungs.

It was selfies galore too ... KK got some, and so did J Lo. It also sounds like some speeches were made -- including one from Sharon that Oprah referenced in her Oprah Daily newsletter.

If the in-person tributes sound impressive ... they're nothing compared to the countless other celebs who wished Oprah a happy birthday on social media -- 'cause there was a lot.

Her longtime BFF, Gayle King, posted a photo of them and wrote, "It’s a big day for all of us who love @oprah ! Happy everything to the girl who lives her best life everyday & does what she can to help everybody else do the same …"

Others social shout-outs came from the likes of Kerry Washington, Alessandra Ambrosio, Lupita Nyong'o, Viola Davis, Garcelle Beauvais and more. Indeed, Oprah's left an impression.