Miley Cyrus Crying in Vegas During First Post-Liam Performance.

Miley Cyrus broke down crying in Vegas yesterday while she performed a song rumored to be about her break up with Liam Hemsworth.

Miley twerked it up on stage at the iHeartRadio Music Festival - but the tears started flowing hard once she began singing "Wrecking Ball."

We heard they recently called it quits,  and Liam has gotten tight with telenovela actress Eiza Gonzales, who BTW is crazy hot.

Despite the cry-fest. Miley cleaned up for her second performance of the night. The pic above was what she wore.

Watch video after the cut.