Daniel Murphy was selected in the 13th-round (394th overall) of the 2006 draft. He’s a third baseman by trade but debuted in the major as a left fielder. He later played first base before settling in at second the past two seasons. Now, Murphy is back at first with the demotion of Ike Davis. Through it all, Murphy’s bat has been a constant in the Mets’ anemic lineup and he has emerged as a core player in the team’s massive retooling. “Daniel Murphy is a professional hitter,” manager Terry Collins said. Although Murphy has had a few hiccups in his move back to first base, including a costly error on Tuesday night against the Cardinals and a missed tag on a pickoff on Saturday against the Cubs, his bat his been invaluable this season, especially in the clutch. Murphy is hitting .308 (16-for-52) with runners in scoring position and an even more impressive .522 (12-for-23) with runners in scoring position and two outs. He went 2-for-2 with two RBI in a 6-3 loss to the Cubs on Friday night and slammed a key double in the Mets’ 5-2 defeat on Saturday. “I’m just trying to center the ball, just trying to hit it hard,” said Murphy, who is hitting .285 with 31 RBI, including a team-leading 20 doubles and five homers. “I’m not trying to leave the ballpark or anything like that.