They are arguably the most underappreciated players on any major-league roster. And yet they are often called upon in the biggest situations, and expected to perform in the tensest of circumstances. They are the left-handed relievers, and Tuesday both of the Diamondbacks’ new lefties made their debuts, with Tony Sipp getting the final out in the top of the sixth and Matt Reynolds recording a 1-2-3 ninth. After starter Trevor Cahill allowed a two-run homer to Matt Holliday to put the Cardinals up 3-1 and then gave up a single and walk with two outs, Sipp needed just one pitch to retire lefty Daniel Descalso on a fly ball to center to end the inning. Three innings later with the score 6-1, Reynolds faced one lefty in Matt Carpenter and then two righties in Holliday and Allen Craig, retiring all three. Diamondbacks manager Kirk Gibson said that arrangement could stick in the early part of the season, with Reynolds coming in for innings at a time and Sipp being viewed more as a left-handed specialist. “I think over the course of the year, maybe Reynolds would throw more extended periods,” Gibson said before Wednesday’s game. “He’d be a guy we’d not hesitate to stretch out to two innings. Sipp maybe not as much. That’s the way I see it now. It could change.” In seven combined seasons, neither Sipp nor Reynolds has had a year in which he had more innings than appearances, meaning they were often used for just one or two batters. In baseball, those kinds of specialists are referred to as “LOOGYs” (Lefty One-Out Guys), a not-always-flattering term that neither pitcher is quick to identify with. “I try not to lump myself in with that,” Sipp said. “I’ve always been a competitor, whether it’s right- or left-handed (batters). But right now, my job is to go in and get that lefty out. Hopefully I can prove that I can handle more of a workload later on.” Added Reynolds: “It’s just whatever. It’s the term that’s been handed down. My buddies get a kick out of that. But it is what it is. I don’t think anything’s going to change.”