LONDON (AP) — Vasyl Lomachenko of Ukraine opened his second Olympics in the same dominant style that made him the best boxer in Beijing, overwhelming Dominican lightweight Wellington Arias in a 15-3 victory Thursday.

Anthony Ogogo kept the British boxing team unbeaten at home with an unlikely victory over world champion middleweight Ievgen Khytrov of Ukraine, the top seed in the Olympic tournament. Ukraine filed a protest of the result after Ogogo won a close fight on the judges' second tiebreaker, a rare occurrence in amateur boxing, but it was swiftly rejected.

Germany's Stefan Haertel also pulled an upset, beating heavily favored Irish middleweight Darren O'Neill to advance to the quarterfinals at ExCel arena. O'Neill's defeat was Ireland's first loss in London.

Although Prince Philip, Prince Edward and wife Sophie attended the afternoon session to cheer on Ogogo, Lomachenko was the star of the show. The 24-year-old with sublime hand speed and devastating power was the king of the Beijing ring four years ago, winning featherweight gold and collecting the Val Barker Trophy as the games' best boxer.

He won two world championships in the past three years while declining opportunities to turn pro, but his performance against Arias showed every Olympic lightweight is still chasing him.

Fighting in the first bout of the day, Lomachenko waited roughly 50 seconds to throw a real punch — but when he did, it was a vicious uppercut that slipped through Arias' raised defense and snapped his neck back before the Dominican even knew it was coming.

Lomachenko warmed up after that, firing speedy strikes and fluid combinations that resulted in standing-eight counts for the overwhelmed Arias in each of the first two rounds. Lomachenko cruised to the win in front of cheering fans before declining to speak to the media afterward, just as he did in Beijing, only saying, "Thanks."

"I lost against the best," Arias said through a translator. "He gave me good shots because I didn't move much. It was an experience I'll never forget."

Lomachenko's next bout is against promising Puerto Rican Felix Verdejo, who beat Tunisia's Ahmed Mejri 16-7.

Ogogo delighted another raucous home crowd with a gutsy performance against Khytrov, the world champion middleweight who entered the ring wearing a military beret.

The Brit ducked and dodged away from Khytrov's superior power for three rounds, scrambling to score points from odd angles and on counterpunches. Khytrov forced Ogogo to take two standing-eight counts late in the second round, yet Ogogo still led 11-10 after two rounds before a close third.

The final score was 18-18, sending the decision to the tiebreaker in which every punch scored by all five ringside judges is totaled — but that total finished 52-52. The second tiebreaker is a simple vote for the winner by the five judges, and Ogogo crumpled to his knees after learning he had won, later leaping up and down in the ring in celebration. The breakdown of the final vote was not released.

"I just believed in myself," Ogogo said. "Nobody thought I was going to win that fight, apart from me, my team, my family. It meant a lot to me, as you could see from my celebration. I've been on the other end of that so many times. I needed that, and I deserved that."

Although Ukraine protested the result, Khytrov said he had no problem with the decision, praising Ogogo as a tremendous fighter.

"I am not angry," he said. "Anthony is good. I say good luck to him."

Haertel controlled his bout with O'Neill, a former European champion who couldn't penetrate the promising German's strong defense.

"He has more experience, so it was a good win for me," Haertel said. "The strength of this Berlin team is that we all have good defense."