Didi provides bench strength

BOSTON — Didi Gregorius spent almost nine innings on the Yankees bench Saturday, held out of the lineup because lefty Chris Sale started for the Red Sox.

But when the shortstop finally got into the game in the top of the ninth of a 4-1, 16-inning win, he ended up with a full day.

The shortstop, who was stuck in an 0-for-15 rut entering the game, delivered the go-ahead single in the 16th at Fenway Park.

Facing Doug Fister with Jacoby Ellsbury and Chase Headley on the corners, Gregorius smacked a single up the middle to spark the threerun inning.

“I was just trying to hit the ball up the middle,’’ Gregorius said after the 5-hour, 50minute game was over. “The infielders were in. I’ve been struggling lately with guys in scoring position and finally came through today.”

It came at a crucial time, with the Yankees in the midst of a brutal stretch and in dire need of a victory.

Normally, those moments don’t come nearly six hours into a game that you started on the bench.

“It’s always tough in those situations, whether you’re [starting] or not,’’ Gregorius said. “Especially in the late innings. … But you never know, so you’ve got to stay ready.”

Austin Romine and Gary Sanchez added RBIs to provide some insurance as the Yankees avoided a third straight loss.

“We needed this a lot,’’ Gregorius said. “We never gave up and everybody was battling.”

Gregorius wasn’t the only late entry to make an impact. Ellsbury didn’t enter until the top of the ninth, either, as a pinch runner for Starlin Castro

Castro, still somewhat slowed by the strained hamstring that he only returned from on Saturday, clearly was protecting the injury both on a second-inning double to right when he coasted into second and on a grounder to short in the ninth, when he reached thanks to Xander Bogaerts’ throwing error.

Manager Joe Girardi said he yanked Castro because he represented the tying run and Ellsbury is the superior runner.