How an unexpected A’s roster move changes the starting rotation picture

Daniel Mengden #33 of the Oakland Athletics reacts after giving up a solo home run to Robinson Cano #22 of the Seattle Mariners in the first inning during their game at Safeco Field on Sept. 24, 2018 in Seattle, Washington.MESA, Ariz. — A pitcher originally tabbed as a near-lock for the A’s Opening Day starting rotation appears to be out of the mix.

Daniel Mengden was optioned to Triple-A Las Vegas Monday morning. It’s a move that comes as a bit of a surprise after the right-hander had entered spring camp as the likely No. 4 starter.

There are a couple of factors that likely played into this decision.

Because Mengden has not accrued enough major league service time, he has a fourth minor…