MIAMI — After a so-so spring training, Masahiro Tanaka will take the mound at Yankee Stadium on Monday as the Opening Day starting pitcher.

The assignment wasn’t a surprise. But Tanaka’s lack of oomph during his spring training outings was, at least to manager Joe Girardi. He felt the need to challenge his ace to pick it up before he committed to naming him the Opening Day starter.

On Saturday, Tanaka admitted he went into spring training with “worry” after having surgery in the offseason to remove a bone spur in his elbow. That could be the reason he held back during his spring training appearances.

“Yes, there was a little bit of worry just because it was my first time getting surgery like that,” Tanaka said through his translator. “So, in a sense, there was a little bit of worry. But I think I was able to build myself up strongly during spring training and I feel like I’m in a good place right now.”

Tanaka had a 7.36 ERA in four official spring training starts. His last outing, in which he allowed one run and seven hits in four innings to the Phillies on Tuesday, isn’t included in those stats because the game didn’t go five innings due to rain.

Still, Tanaka showed Girardi enough to earn his second straight Opening Day nod.

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“It was a gradual process, but I think that very last outing kind of gave me the confidence to go into the season,” Tanaka said. “I think I was able to get some good work in leading up to today. Yes, I am ready for the season.”

Tanaka will be opposed by defending AL Cy Young award winner Dallas Keuchel in a repeat of last year’s wild-card playoff game, which the Astros won, 3-0.

“Our season ended against them last year, obviously,” Tanaka said. “I know that I’m facing a really good pitcher as well, so I’m going to go out there and try to do my best just to contribute to the team.”

No. 4 starter Luis Severino finished a strong spring training by allowing two runs (one earned) in five innings in the Yankees’ 2-1 loss to the Marlins. Severino, who gave up three hits, walked one and struck out six, finished with a 3.38 ERA.

No. 5 starter CC Sabathia will throw in a minor-league game on Sunday in Tampa before re-joining the Yankees in New York on Monday. Sabathia’s first start is scheduled for Saturday in Detroit.