Argentina’s Marcos Maidana stopped Ortiz early in the sixth round of an action-packed fight Saturday night, leaving one of the sport’s top prospects pulverized and chastened. The 140-pound bout featured five knockdowns and several wild momentum swings that both thrilled and stunned a Staples Center crowd of 8,600 expecting to witness another step in the evolution of the 22-year-old Ortiz, a charismatic slugger ticketed for stardom by promoter Oscar De La Hoya.

Instead, the fans marveled at a remarkably resilient U.S. debut by Maidana (26-1, 25 KOs) a heavy-handed 140-pounder largely unknown outside his native land and Germany, where he has fought six times in the last two years.

Maidana was knocked down three times in the opening two rounds, yet rallied with a devastating right hand that turned Ortiz’s face into a mess. After Ortiz stumbled to the canvas early in the sixth, the ringside doctor stopped the fight.

“I knew I was fighting against the local guy, and I had to knock him out,” said Maidana, whose only previous loss was a contentious split decision to Andreas Kotelnik earlier this year. “I went down, but I got up because I have a big heart. I saw that Victor felt my punches, and I said, ‘I know I can win this.”’

Ortiz (24-2-1), who held a comically large bag of ice to his swollen face afterward, acknowledged he entered the ring thinking about the bright lights, the chanting fans and the pressure – everything but Maidana, who also knocked him flat in the first round and then eagerly accepted Ortiz’s invitation to brawl.

“It didn’t hit me until I was on my way to the ring,” Ortiz said. “I was like, ‘Whoa.’ It just really messed with me, and I didn’t perform. … I just fought a dumb fight. I didn’t listen to my corner.”

Although De La Hoya insisted Ortiz still is a budding champion, the Kansas native took too many big shots while fighting with no discernible strategy. Ortiz connected on 42 percent of his 177 punches, but Maidana was much busier with 293 punches, connecting with 23 percent.

“Yeah, he went down,” De La Hoya said. “But he’ll get right back up and fulfill his dream.”

Both fighters moved forward furiously from the opening bell, and Ortiz knocked down Maidana for the first time on a big right hand with about 1:15 left. With the crowd standing and cheering for Ortiz, Maidana landed a right hand that put Ortiz flat on his back.

The crowd was as stunned as Ortiz. The second round was even more electric, with the boxers trading shots until Ortiz knocked down Maidana with a right hook with about 30 seconds left – and then did it again with a shorter version of the same punch right before the bell.

But Maidana landed several big shots in the next three rounds, rocking Ortiz with two powerful right hands in the final seconds of the fifth. Ortiz also developed that big cut, which gaped open when the fight ended 46 seconds into the sixth.

“I came to look to finish him, and that’s what happened,” Maidana said. “He hits very hard, but he doesn’t have a good chin. Definitely he didn’t adjust to my rhythm.”