Hisashi Iwakuma could complicate rotation

SAN DIEGO – It’s about to get crowded in the Seattle Mariners’ rotation – assuming right-hander Hisashi Iwakuma has no problems Tuesday night in his scheduled rehab start for Triple-A Tacoma at Cheney Stadium. Iwakuma is slotted for six innings and 90 pitches in what will be his third rehab start in his ongoing recovery from a strained back muscle suffered in a routine day-after throwing session following his April 20 start. That positions Iwakuma, who won 38 games over the three previous seasons, to rejoin the rotation Sunday in Oakland for the final game of the Mariners’ nine-game trip. Maybe. The Mariners don’t have an obvious opening in their rotation. “It’s a nice problem to have,” manager Lloyd McClendon hedged. “Right now, we’re still in the process of figuring out what we’re going to do when he comes back.” Since staff ace Felix Hernandez and surging rookie Taijuan Walker are unlikely to be affected by any rotation adjustment, the Mariners – barring an injury or a trade – appear to have the following options:  Send either Mike Montgomery or Roenis Elias back to Tacoma.  Shift veteran J.A. Happ to the bullpen.  Implement a six-man rotation.  Keep Iwakuma on his rehab assignment. The decision should clarify later this week when McClendon announces his rotation for the four-game weekend series at Oakland. Monday’s open date in the schedule provides the Mariners with some flexibility. As the rotation currently lines up, Sunday would be Montgomery’s turn, but he has a 2.04 ERA in five starts since his June 2 recall from Tacoma to replace an injured James Paxton. Barring a major stumble Tuesday, when he starts against the Padres in San Diego, it’s hard to imagine Montgomery losing his job. Elias, in contrast, took a pounding in two of his last three starts, which spiked his ERA from 2.79 to 4.35.