LONDON (AP) — Defending champion Zou Shiming of China narrowly advanced to another gold-medal bout with a tiebreaker victory over Ireland's Paddy Barnes on Friday in the first of 20 semifinal fights in the Olympic boxing tournament.

Bantamweight John Joe Nevin of Ireland stunned top-seeded Lazaro Alvarez of Cuba 19-14 to advance to the final against Britain's Luke Campbell, who beat Japan's Satoshi Shimizu 20-11.

Ukraine light welterweight Denys Berinchyk and Mongolia's Munkh-Erdene Uranchimeg put on perhaps the best fight of the tournament, with the relentless Berinchyk rallying from a second-round deficit to score a jaw-dropping 17 points in the third round of a 29-21 victory. Berinchyk will face Cuba's Roniel Iglesias in the final.

Berinchyk will be joined in the finals by heavyweight teammate Oleksandr Usyk, who dominated Bulgaria's Tervel Pulev to earn a gold-medal bout. He'll meet Italy's Clemente Russo, who beat top-seeded Teymur Mammadov of Azerbaijan in yet another hold-filled bout for two boxers whose styles don't please many fight crowds.

Ukraine's powerful team placed a tournament-high five boxers in the semifinals, with lightweight champion Vasyl Lomachenko and the rest fighting Friday night. The Ukrainians are distinctive for more than their boxing acumen and those blue-and-yellow outfits: Both Berinchyk and Usyk cut their hair into a chub, a traditional Cossack haircut featuring a shaved head with one long, flowing lock on top.

Barnes hoped to bounce back from four years of embarrassment after Zou beat him 15-0 in the semifinals in Beijing, and the energetic Irish fighter nearly knocked off the champ. After three rounds of strong exchanges, the bout was scored 15-15, but Zou edged Barnes on the countback tiebreaker that tallies up a more complete total of punches landed.

"I'm not going to cry about it," said Barnes, a personable, popular fighter who spent much of his time in the Olympic village trying to take photographs with famous athletes. "He's a world champion, and he got that for a reason."

While this is the last Olympics for the 31-year-old Zou, Barnes said he wouldn't mind coming back at the 2016 Rio Games, "unless someone offers me a million pounds."

Zou will meet Thailand's Kaeo Pongprayoon in the final after his 13-12 win over Russia's David Ayrapetyan.

Nevin had few problems getting rid of the top-seeded Alvarez, who beat talented U.S. bantamweight Joseph Diaz Jr. in one of the tournament's better fights last week. Nevin even showboated a bit for the hundreds of fans who mobbed the square of his hometown in Mullingar, Ireland, to watch the fight on televisions, doing a little shuffle-step move dubbed the Mullingar Shuffle by his coaches.

"I think he kind of gave up a little halfway into the last round when he couldn't get to me," Nevin said.

Campbell easily took care of Shimizu to set up a rubber match with Nevin. The pair split two recent fights, including a meeting at the world championships.

Campbell's teammate, middleweight Anthony Ogogo, got knocked down and never got rolling in a 16-9 loss to Esquiva Falcao, who will fight Ryota Murata for Brazil's first boxing gold medal. Falcao's brother, Yamaguchi, also reached the light heavyweight semifinals.

Murata, who rallied in the third round to beat Uzbekistan's Abbos Atoev 13-12, will attempt to win Japan's second Olympic boxing gold medal — the first since the 1964 Tokyo Games, when Takao Sakurai won at bantamweight.

Berinchyk and Uranchimeg combined for an all-out brawl, with Berinchyk relentlessly pushing forward while Uranchimeg picked him apart with hooks and counterpunches. Both fighters took numerous clean head shots, but Uranchimeg — who upset Britain's Tom Stalker two days ago — got caught with a combination and a standing-eight count in the third round.

Berinchyk was relentless, recording another eight-count on the dazed Uranchimeg before finishing strong. The serious-faced Berinchyk then did a joyful dance in the ring after advancing to meet Iglesias, whose win over Italy's Vincenzo Mangiacapre wasn't nearly as entertaining.

Usyk had the best showing of the four fighters left in the holding-dominated heavyweight division, where many fights have been booed by fans bored with constant clinches and wrestling. Mammadov and Russo both advanced to the semifinals after holding-plagued victories that drew protests from the losers, but Beijing silver medalist Russo was slightly better than the top-seeded Azeri.