Bob Melvin’s game plan, much like his bullpen, was bare-bones for the nightcap of Wednesday’s doubleheader. The A’s manager had starter Drew Pomeranz and relievers Dan Otero and Jim Johnson at his pitching disposal, with minor league call-up Arnold Leon in reserve if needed. That skeleton crew was handed the load and excelled in a 2-0 victory over the Seattle Mariners that helped the A’s avoid a four-game sweep. Oakland’s bullpen was feeling the effects of recent heavy use, and the need to use five relievers in a 10-inning loss in Wednesday’s opener made the situation more dire. “Three guys took over on the pitching end for us and came up huge,” Melvin said. “Basically we had three guys, and then Leon somewhere for length. They all knew it.” Pomeranz, making his first major league start since July 22 of last season, was terrific. He covered five innings in 68 pitches, allowing just two hits with no walks and five strikeouts. The lefty has impressed in a long relief role so far this season. He came over from Colorado in the Brett Anderson trade with a 4-14 career record and 5.20 ERA, mostly as a starter. But the feeling is there’s untapped potential in his 6-foot-5 frame, and with the back of the A’s rotation having experienced some bumps this season, it will be interesting to see whether Pomeranz gets more chances in a starting role. Melvin declined to address that in the immediate aftermath of the game, but he was impressed.