bristolsarah460.jpgDWTS photo courtesy of ABC

Bristol Palin and partner Mark Ballas steamed up the dance floor on Dancing With the Stars last night with their sexy rumba ... and mom Sarah Palin witnessed the whole thing just rows away!

The 19-year-old mom may give speeches about the importance of abstinence ... but there was no abstaining on the DWTS stage. Wonder what Sarah REALLY thought when her daughter ripped off Mark's shirt during the dance? His abs were hot ... but whoa, get a room!

Unfortunately, even the over-the-top sexy antics didn't earn Bristol high scores. She earned a 32 out of 50. But at least she can say she beat Mike "The Situation" Sorrentino. His trademark abs were in full effect, but those pigeon toes were, too. Props to Sitch for keeping his head up ... even when Bruno Tonioli called his performance "a terrible mess."

The highlight of the night .... Jennifer Grey dancing a near perfect argentine tango which earned her the first 10's of the season. To see young Bristol work it on the dancefloor, watch below. We'll be watching tonight to see who gets the boot!