Texas Rangers closer Joe Nathan gave up back-to-back triples Monday, but the bigger development was the progress of his slider. After the two triples, which accounted for San Francisco’s second run in a 2-1 victory, he found the Giants committing to and chasing his slider. That led to three consecutive strikeouts. Nathan said his arm strength is still lacking, but that it has come later during spring training in recent years. He compiled a 10.29 ERA in seven spring games last year and a 9.72 in 2011, his first year back from Tommy John surgery. “It is never there early, so it’s not a shock,” Nathan said of his fastball. “Do I like it that way? No. But it has always come back and I just trust that it will again. … But I thought today was a very productive day. I saw my slider having the right shape. It wasn’t too big and guys were committing to it. That lets me know I’m getting close to where I need to be.”