CARSON, California: Gennady Golovkin stopped Marco Antonio Rubio in the second round Saturday night, defending his WBA middleweight title with his 18th consecutive stoppage victory.

Golovkin (31-0, 28 KOs) punctuated his brief West Coast debut with a crushing left hand to the forehead. Rubio tumbled to the canvas and couldn’t get his wits together in time, the fight ending 1:19 into the second round.

“I liked the fight,” Golovkin said. “Rubio, he does not step back. He is a good fighter. I respect him. It was a very hard punch.”

The flourish of Golovkin’s final blows rocked StubHub Center, which was packed to standing-room-only capacity with fans of the Kazakh-born, California-trained middleweight who has become one of the sport’s most charismatic stars. The crowd of 9,323 — easily the largest turnout for a boxing event at the outdoor stadium — chanted “Triple G!” and leaped to its feet for the stoppage.

“Those cheers were not only for the fighter, but for the person he has shown to be,” said Abel Sanchez, Golovkin’s trainer.

Golovkin battered Rubio (59-7-1) throughout his 12th title defense, hurting Rubio earlier in the second round with a right hand and a left uppercut.

A raucous sellout crowd in the outdoor stadium chanted the name of the Kazakh-born, California-trained middleweight who has become one of boxing’s most charismatic stars.

“I felt I hurt him with the left hand, and the uppercut was when he was very badly hurt,” Golovkin said. “I knew I had him. ... I was happy he came forward. He fought Mexican style, and he tried to hurt me, but my power was too much for him tonight.”

Golovkin won Rubio’s WBC interim belt, which means the winner of WBC champion Miguel Cotto’s upcoming bout with Canelo Alvarez must either fight Golovkin or vacate the title. Golovkin has trouble attracting the world’s biggest 160-pound names, so he hopes to clean out the division by winning every belt.

“He’ll fight anyone, whoever we can get in the ring,” promoter Tom Loeffler said.

Rubio briefly complained that the knockout punch was illegal, although television replays clearly contradicted him.

“Gennady is a great champion,” Rubio said. “He hit me hard, but it’s not the hardest I’ve been hit. I came to fight, to put on a good show. I got up, but the referee decided to stop it.”

The StubHub Center crowd of 9,323, easily the largest turnout for a boxing event at the outdoor stadium, chanted “Triple G!” and leaped to its feet for the stoppage.

Rubio missed weight for the fight on Friday by nearly 2 pounds, costing him the chance to fight for both titles. He entered the ring weighing 181 pounds, but Golovkin floored him with the same relentless style that has been too much for every middleweight opponent to date.

Golovkin landed 28 power punches in just over four minutes of ring time against Rubio.

Walters stops Donaire in 6th, wins 126-lb title

In the undercard, Nicholas Walters stopped Philippine-born Nonito Donaire with a second left in the sixth round, winning the WBA featherweight title in dramatic fashion.

Walters (25-0, 21 KOs), a fairly unknown fighter from Jamaica, punctuated his breakthrough performance by knocking down Donaire (33-3) for the first two times in the four-division champion’s career.

After Donaire swung and missed with a huge left hand late in the sixth, Walter caught him above the ear with an overhand right. Donaire fell face-first to the canvas, and though he beat the count, he couldn’t continue in his second loss in four fights.

Walters also knocked Donaire down to one knee in the third round with an uppercut, and he absorbed Donaire’s biggest punches in an impressive all-around performance that thrilled the sellout crowd for Gennady Golovkin’s middleweight title bout against Marco Antonio Rubio.

“We worked hard for this victory,” Walters said. “Donaire is a super great champion. I know I have to respect him, and that’s what I did. He caught me with a few shots.”