Middleweight champion Gennady Golovkin didn't waste any time with a substitute opponent on Saturday night, dropping and stopping stand-in Vanes Martirosyan in round two of a scheduled 12-rounder at the StubHub Center in Carson, California.

The HBO-televised main event ended at 1:53 of the second.

Golovkin had been scheduled for a blockbuster Cinco de Mayo rematch with Canelo Alvarez in Las Vegas, but that event was scuttled when the red-haired Mexican pulled out after a pair of failed drug tests. He was subsequently suspended for six months by the Nevada Athletic Commission. Golovkin and Alvarez had fought to a draw last September.

Martirosyan got the date with less than four weeks' notice and entered having not fought in nearly two full years since a loss to Erislandy Lara at 154 pounds. He's not won a fight since defeating Ishe Smith in 2015, but was nevertheless ranked first at 154 pounds by the WBC.

It was Golovkin's second career fight at the StubHub Center and his second abrupt exit. He TKO'd Marco Antonio Rubio in two rounds there in 2014.

This time around, the Armenian-born challenger stood his ground in the first three minutes and landed six power punches to the champion's five. Golovkin began asserting himself early in the second, however, and drove Martirosyan to the ropes with a right uppercut. He then landed a pair of straight rights and two left hooks to drive Martirosyan to the floor.

Another shot appeared to connect as Martirosyan touched the canvas, but referee Jack Reiss didn't penalize Golovkin. Martirosyan was initially on one knee, then pitched forward to a prone position on the floor. He was back to his knees as Reiss got late in the count, then went back down as he got to 10.

It was Golovkin's 17th defense of the IBO championship he won in 2011. 

The fight's promoters billed it as a record-tying 20th defense, but the WBA title that Golovkin won in 2010 was that organization's second-tier belt. He didn't become the WBA's full-fledged belt-holder until 2014, then added the IBF title in 2015 and the WBC championship when Alvarez relinquished it in 2016.

The IBF title was not at stake on Saturday because the group refused to sanction the bout.

Golovkin is widely expected to meet Alvarez in a September rematch after Alvarez's suspension ends later this summer, but he got a loud ovation from a near-capacity crowd when he claimed "I want everybody" in an in-ring interview after the fight.

Golovkin landed 36 of overall 84 punches (42.9 percent) in the abbreviated night's work, while Martirosyan connected with 18 of 73 (24.7 percent).

A member of the 2004 U.S. Olympic team, Martirosyan fell to 36-4-1 in a 13-year pro career. He turned 32 on Tuesday and is 4-4-1 in nine fights since beginning his career with 32 straight wins.

"That's the hardest puncher I've ever faced," Martirosyan said.

Undisputed women's welterweight champion Cecilia Braekhus made history in the final run-up to the main event, defeating challenger Kali Reis via unanimous decision in the first women's bout aired on HBO.

Braekhus, who holds the IBF, IBO, WBA, WBC and WBO title belts, was a 97-92 winner on one official scorecard and a 96-93 winner on the other two in spite of suffering the first knockdown of her pro career in the seventh round.

CBS Sports saw Braekhus a 97-92 winner.

Reis, a former women's middleweight champion, was outworked and outskilled through the first six rounds before dropping Braekhus with a short, straight right hand along the ropes in the seventh. 

The champion bounced right up and appeared more surprised than hurt, but the bout was surely more competitive down the stretch.

Some of the crowd, in fact, booed the announcement that Braekhus had won.

Afterward, Braekhus labeled Reis an "amazing and tough fighter."

On the non-televised undercard:

  • Blue-chip lightweight prospect Ryan Martin passed his most significant professional test to date, defeating skidding veteran Breidis Prescott by a wide 10-round verdict. Martin, now 22-0, was a 79-71 winner on two scorecards and a 77-73 winner on the third against Prescott, who's now 31-13. The Colombian slugger won his first 21 fights -- including a first-round KO of future world champion Amir Khan – but is 10-13 since 2009. 
  • Ruslan Madiev, a super lightweight from Golovkin's native Kazakhstan, defeated Jesus Perez by 10-round decision in a meeting of unbeaten fighters. Madiev, 25, won nine, seven and seven rounds across three scorecards against Perez to reach 12-0, while Perez fell to 21-1.  
  • California-born teen featherweight Jesse Rodriguez stayed unbeaten as a pro with a third-round KO in a scheduled six-rounder against 48-fight veteran Armando Vazquez. Rodriguez (6-0), who turned 18 in January, ended matters at 2:18 of the third. Vazquez is 25-22-1.
  • Welterweight Brian Ceballo improved to 2-0 with a unanimous four-round decision over Nam Phan. All three judges saw Ceballo a shutout winner with 40-36 scorecards over Phan, who's 0-6-1 since beginning his career with three consecutive victories.

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