Rodriguez continually fired kicks at the former lightweight and welterweight champ, and shortly into round two, he sent Penn to the deck with a front kick. The star attempted to defend the flurry of punches that Rodriguez sent from above, but after several moments, the fight was called.
The 38 year-old Penn was fighting for the first time since 2014, when he was stopped by Frankie Edgar.
Here are the results for UFC FN 103, which was hosted by Phoenix, Arizona.
Yair Rodriguez def. B.J. Penn via TKO (punches) R2, 0:24
Joe Lauzon def. Marcin Held via split decision (27-30, 29-28, 29-28)
Ben Saunders def. Court McGee via unanimous decision (29-28, 29-28, 29-28)
Sergio Pettis def. John Moraga via unanimous decision (29-28, 29-28, 30-27)
Drakkar Klose def. Devin Powell via unanimous decision (30-27, 30-27, 30-27)
Augusto Mendes def. Frankie Saenz via split decision (29-28, 28-29, 29-28)
Aleksei Oleinik def. Viktor Pesta via submission (Ezekiel choke) R1, 2:57
Tony Martin def. Alex White via unanimous decision (30-27, 30-27, 30-27)
Nina Ansaroff def. Jocelyn Jones-Lybarger via submission (rear-naked choke) R3, 3:39
Walt Harris def. Chase Sherman via knockout (punches) R2, 2:41
Joachim Christensen def. Bojan Mihajlovic via TKO (punches) R3, 2:05
Cyril Asker def. Dmitrii Smoliakov via TKO (punches) R1, 2:41