Lip Sync Battle: Grandfathered's Christina Milian and Josh Peck Face Off with Justin Bieber Songs

This week's Lip Sync Battle brought out Grandfathered co-stars Christina Milian and Josh Peck to face off against each other. And the theme of the night? Bieber, baby!

Milian, who has a role in Fox's upcoming Rocky Horror Picture Show TV musical, opened the first round strong with Justin Bieber's "Baby." "This is for all those boys who broke your heart the very first time," she told the audience. Then came Peck's turn and, naturally, he opted for Bieber's "What Do You Mean?" He even managed to cry at the end to give it that extra oomph. Watch a clip here:

The intensity ramped up in the second round as Milian pulled out all the stops for Jennifer Lopez's "Waiting for Tonight." She stepped onto the stage in a revealing black top and black leather pants and channeled her "inner J.Lo." And she certainly succeeded. But we hadn't seen anything yet: For his performance of Sisqo's "Thong Song," Peck sported an all-white sleeveless, oversize suit and even a lime green "mankini." Milian may have been inspired by Lopez, but Peck did an impressive job of channeling Magic Mike—and the audience was all about it. John Stamos (his TV dad) would be so proud.

Watch Milian perform "Waiting for Tonight" and Peck take on "Thong Song" in the video above.