Sergey Kovalev knocked out Nadjib Mohammedi in the third round of their light heavyweight title bout on Saturday, barely breaking a sweat in his first appearance as a headline fighter in Las Vegas.

The 32-year-old hard-hitting Russian floored the challenger once in the second round at the Mandalay Bay hotel before finishing him off late in the third, showing why he has bulldozed his way through the 175-pound (79-kilogram) division.

The undefeated Kovalev improved to 28-0-1 and has now knocked out 11 of his last ­dozen opponents. It was the 25th knockout of his professional career.

Kovalev fought on an ­undercard in Vegas four years ago but this was his first ­opportunity to showcase himself in a main event in the city of lights.

The WBO, WBA and IBF champion used Mohammedi, of France, as target practice from the opening bell, landing overhand rights at will in a ­brutally one-sided contest.

The end came when Kovalev caught Mohammedi with a right hand, left hook combination to the left side of his face that dropped the challenger.

The Frenchman (37-4, 23 KOs) got up at the count of nine but the referee quickly waved his arms, putting an end to the slaughter at 2:38 of the third round.

Kovalev tried to prolong the fight and even urged ­Mohammedi, 30, to get up off the canvas after the second knockdown.

Mohammedi became Kovalev's mandatory opponent following a seventh-round knockout of Anatoliy Dudchenko in June.

Kovalev's goal is to hold all four light heavyweight belts but to do that he needs to fight ­Canadian Adonis Stevenson, who has the one belt, the WBC, that the Russian doesn't.

But with no deal for a Stevenson fight, Kovalev could end up fighting another Canadian, Jean Pascal, in a rematch of their March showdown.

Pascal fought on the undercard Saturday night, winning a controversial unanimous ­decision over the tough Yunieski Gonzalez.

Many in the crowd thought Gonzalez won the fight but Pascal landed 36 percent of his punches to just 26 percent for Gonzalez and was given the ­decision on all three judges' score cards.