The moment Ron Gardenhire first saw Oswaldo Arcia’s swing in spring training, the Twins manager became a big fan. Gardenhire has been committed to finding a place in the lineup for the rookie outfielder’s bat ever since Arcia was called up for good last month. That mean putting up with the ups and downs rookies go through. But Gardenhire was not going to let Arcia waste on the bench. Arcia has been particularly precocious this week, cutting down on his swing with two strikes and shooting the ball to the opposite field. “I like the first swing, personally,” Gardenhire said Thursday. “I want the kid to swing.” Arcia celebrated his 22nd birthday Thursday by giving the manager what he wanted. Arcia’s triple in the fifth inning and two-run home run in the sixth were the key blows in the Twins’ 5-3 victory over Boston that helped them win three out of four games at Fenway Park for a second consecutive year. The Twins headed home with a 5-5 record on their 10-game road trip and with their record back over .500 at 16-15. They are still trying to find their way offensively. They batted .239 in April with a .671 on-base-plus-slugging percentage, hitting 15 home runs. May has been better, as they were hitting .278 entering the game with a .821 OPS. But they know they have left some runs on the bases. “You look at some of the guys in our lineup that have less than two years of experience,” first baseman Justin Morneau said. “Mistakes are going to happen. That is how you learn.”