By Larry Fine

SAN FRANCISCO (Reuters) - Giant-killers Puerto Rico ended Japan's World Baseball Classic reign on Sunday, combining a strong pitching effort with the power of Alex Rios to win their semi-final showdown 3-1 at AT&T Park.

Rios crushed a towering two-run homer in the seventh inning off reliever Atsushi Nohmi to break open a taut pitchers' duel and give Puerto Rico a 3-0 lead as Japan lost a chance to extend their domination of the world's top international tournament.

"We're really proud of what we've done," said Rios, whose team eliminated favored powers Venezuela in the first round, the U.S. team in the second round and now the two-time defending champions in the semi-finals.

The blow by Rios brought his team mates pouring onto the field to celebrate with him after he touched home plate.

Mario Santiago, who pitched last year in the South Korean professional league, was masterful in retiring the first 10 batters of the faced and protecting a 1-0 first-inning lead on Mike Aviles's run-scoring single into the fifth inning.

"I know a bit about the Japanese hitters," said Santiago, who trained in Japan last year. "I've seen them in Japan. I know what they're like and what they don't like."

He was followed by five relievers with Fernando Cabrera notching the save, setting off a wild celebration in the middle of the diamond after Angel Pagan gloved Kazuo Matsui's fly ball to center for the final out.

Japan, winners of the first two WBC titles in 2006 and 2009, squandered their best chance in the eighth on a critical base-running gaffe.

After a one-out run made it 3-1 with men on first and second, Seiichi Uchikawa broke for second base on a pitch to Shinnosuke Abe, while lead runner Hirokazu Ibata held his ground. Catcher Yadier Molina ran all the way toward second to tag out Uchikawa, and Abe then grounded out to end the threat.

Japanese manager Koji Yamamoto said he had given a sign for a double steal, thinking the baserunners had a good chance considering the slow delivery of reliever J.C. Romero.

NO REGRET

"Ibata's start was a little delayed," explained Yamamoto. "It failed, but I don't regret the attempt."

Japan had other opportunities, leaving runners in scoring position in the fourth, fifth and sixth innings but could not break through until Takashi Toritani tripled in the eighth and scored on a single by Ibata before the baserunning blunder.

"Our opponent was really superior, both in pitching and in hitting," the Japanese manager said. "So we were cornered in a sense."

Puerto Rico manager Edwin Rodriguez said his team knew what their performance meant to their countrymen.

"We know that there's a lot of people down in Puerto Rico watching and this win is huge," he said. "The way that these guys have been playing and performing is a huge accomplishment for the people in Puerto Rico."

Puerto Rico will play the winner of Monday's semi-final between unbeaten Dominican Republic and the Netherlands, and the WBC will crown a new champion on Tuesday.

(Editing by Amlan Chakraborty)