By Alan BaldwinRIO DE JANEIRO,(Reuters)-Claressa Shields brought one gold medal to the ring with her and left with two hanging around her neck after retaining her Olympic middleweight title and making U.S. boxing history yesterday.As a gesture of confidence, having the 2012 gold at hand in the expectation of showing it off with another took some beating.But so too does Shields, who has not lost a fight since 2012 and is her country’s first double boxing champion in 112 years.“At London I knew I was going to win and I knew I was going to win here,” Shields told reporters after the unanimous decision over Nouchka Fontijn of the Netherlands.“I’ve worked so hard to be here. You know not everybody can be an Olympic gold medalist. I’m a two-time Olympic gold medalist. Oh my god, I can’t believe I just said that,” she exclaimed.Shields knew long before the result was confirmed, and the winner’s hand raised by the Vietnamese referee, that the gold was hers.Climbing out of the ring after the announcement, she ran around the arena with the U.S. flag held aloft before wrapping it around her.TWO TOGETHEROn the podium, she slipped the gold won in London four years ago around her neck to stand and sing the anthem with the two together.“I just wanted to win the first two rounds clear, that’s all I wanted, when I came back to the corner they were saying you got that round, you got that round. I said I have to be smart,” she said of the fight.Shields won the first three rounds 10-9 10-9 10-9 but the fourth was closer, with two of the judges giving it to her Dutch opponent.Fontijn’s medal was the first by a Dutch boxer since heavyweight Arnold Vanderlyde and light-middleweight Orhan Delibas won bronze and silvers in 1992.Kazakhstan’s Dariga Shakimova and China’s Li Qian took the bronze medals as losing semi-finalists.The last American boxer to win two gold medals was Oliver Kirk, who claimed bantamweight and featherweight titles at the same 1904 St. Louis Olympics, where only U.S. boxers took part.Women’s boxing was introduced to the Olympics in 2012 and Shields, unbeaten since then, follows Britain’s Nicola Adams – who successfully defended her flyweight title on Saturday – as a double champion.