Sarah Michelle Gellar & Selma Blair -- Awesome Intentions!! Sucking Face While Reese Witherspoon Watches

Sarah Michelle Gellar and Selma Blair recreated their epic "Cruel Intentions" make out scene last night -- and it was just as epic ... 16 years later.

Reese Witherspoon made it a full reunion -- but she kept her tongue in her mouth -- as the former co-stars went to a musical parody of "Cruel Intentions" that plays in Hollywood.

The ladies seemed to have a great time ... Reese even called it her "best girl night of the year.”

It gets our vote too, Reese ... based on the kiss alone.