Sergey Kovalev KOs Gabriel Campillo

UNCASVILLE, Conn. -- Sergey Kovalev has been building an underground reputation as one of the most dangerous finishers in the light heavyweight division.

After stepping up in class against former titlist Gabriel Campillo on Saturday night at the Mohegan Sun Arena, the fighter known as "Krusher" did little to disprove the hype after an explosive third-round TKO.

Kovalev (20-0-1, 18 KOs), 29, and a native of Chelyabinsk, Russia, who fights out of Fort Lauderdale, Fla., was able to get to the usually elusive Campillo (21-5-1, 7 KOs) early and often, continually backing him up in the opening round with furious combinations.

Campillo, known as a slow starter who looked sluggish throughout the fight, was hurt early in the third round and staggered into the corner. The native of Spain covered up before being dropped with a left hook from Kovalev, one of three knockdowns in the round.

"I saw that he was like swimming after some punches (early in the third round)," Kovalev said. "I knew I must finish early because he is an experienced guy. If we let him go, it could have gone to the judges' decision and all of that nonsense. And we didn't want any problems. "

Kovalev floored Campillo for good later in the round on a straight right hand, giving referee Michael Ortega no need to count with the end coming at 1:30.

It was the sixth straight knockout for Kovalev, sandwiched around a two-round technical draw in 2011. The loss was the second straight for Campillo, who dropped a debated split decision to titlist Tavoris Cloud last February.

Fireworks erupted during and after a scheduled 10-round middleweight bout between Curtis Stevens and Elvin Ayala in the co-main event.

Stevens (23-3, 17 KOs), 27, a native of the Brownsville in Brooklyn, N.Y., badly hurt and floored Ayala on a counter-left hook in the first minute of the opening round. Ayala (26-6-1, 12 KOs), 32, regained his feet before Stevens swooped in for a second knockdown, causing referee Tony Chiarantano to call for the bell instantly at 1:10.

As Stevens celebrated on the second rope just seconds later, a member of the crowd rushed the ring and attacked him from behind, setting off a melee in the center of the ring before order was quickly restored.

"I was on the rope and I felt somebody on my back," Stevens said. "I thought it was one of my cousins or uncles. I turned around and he just grabbed me and pulled me down from the ropes. I didn't get hit or anything."

The ring intruder was a cousin of Ayala's, according to promoter Main Events, and was arrested after the disturbance.

"I think that was Ayala's (relative) and that's his blood brother," Stevens said. "I could understand his feelings or emotions he would have. When someone has in they mind their brother is going to do something, the emotions oversee things. It's boxing. He's human, I'm human."

Both Ayala and Stevens had exchanged words throughout the heated build-up during the week of the fight.