LAS VEGAS >> Demetrious Johnson retained his flyweight title Saturday night at UFC 178, submitting Chris Cariaso in the second round.

Johnson easily scored a takedown in the first round and stunned Cariaso with a looping right hook, followed by a knee to the jaw as the horn sounded to end the round.

Johnson kept the pressure on in the second and gained top control after Cariaso’s slip. Johnson swiftly maneuvered into side control, landed a few elbows and secured a Kimura, forcing Cariaso to tap out at 2:29 of the second.

“I felt good. It was a great fight,” Johnson said. “I’m just trying to get better at my ground game.”

Johnson improved to 21-2-1 with his fifth straight title defense. Cariaso dropped to 17-6.

In the co-main event, lightweight Donald Cerrone moved closer to a title shot with a unanimous decision over Eddie Alvarez. Cerrone used powerful leg kicks to wear down Alvarez, winning 29-28 on all three scorecards.

“There’s no quit in this dog,” Cerrone said. “If you’re going to beat me, you better do it in the first.”

In a battle of rising featherweights, Conor McGregor made short work of Dustin Poirier, earning a TKO victory in the first round. McGregor improved to 16-2, and Poirier fell to 16-4.

“I don’t just knock them out, I pick the round,” McGregor said. “When featherweights get hit by me it’s a whole new ballgame.”

Yoel Romero survived a back and forth brawl to beat Tim Kennedy by TKO, and No. 1 women’s bantamweight contender Cat Zingano moved into position for a title shot with a third-round TKO over Amanda Nunes.

Former bantamweight champion Dominick Cruz highlighted the undercard with a first-round TKO over Takeya Mizugaki. Jorge Masvidal, Stephen Thompson, Brian Ebersole, Kevin Lee and Manvel Gamburyan also won.