BOSTON — Such is the unpredictable nature of this 2017 Boston Red Sox team that David Price has been hardly missed. But when the trainer went out to the mound Friday night to check on Drew Pomeranz, there was a gasp at Fenway Park.

Who knew Pomeranz would become so valuable?

The left-hander left Friday night’s game in the fourth inning because of back spasms. We will have to wait to see if this will be a lingering problem.

Pomeranz pitched 31/3 scoreless innings. That gives him a 2.61 ERA since May 20. Only Cleveland’s Corey Kluber (1.85) has been better among American League starting pitchers (Chris Sale is at 2.72).

“He’s more certain with his pitch mix as far as attacking the strike zone,” Boston Manager John Farrell said. “He’s worked at a quicker pace.

“And I think, as he has put (positive) outings under his belt, he’s grown with a lot of confidence.”

The pace used to be slow, the strike zone elusive. Pomeranz’s pitch counts elevated fast. There was the notorious May 20 start where Pomeranz was seen arguing with Farrell in the dugout because he was yanked after throwing 97 pitches in four innings.

Since then, Pomeranz has been in control.

“He’s done an outstanding job with men on base,” Farrell said. “He’s found a way to navigate through a potential big inning and has minimized it.

“That’s been one of the biggest things that has shown up – his ability to get out of the big inning.”

On Friday night, the Yankees were 1 for 8 against Pomeranz with runners on base, and the hit was a harmless Aaron Judge single with two outs in the third inning.

With runners on first and second, Pomeranz struck out Gary Sanchez on a wicked curveball that dropped like a shot put into the dirt as Sanchez swung through it.

It was Pomeranz’s second strikeout of Sanchez. The Yankees slugger was hitting .462 (6 for 13) with three home runs against Pomeranz.

Pomeranz got Sanchez to chase a curve in the first inning, too. His other two strikeouts came on elevated fastballs, against Aaron Hicks and Didi Gregorius.

Pomeranz began the game with six straight fastballs to leadoff hitter Brett Gardner, who lined a single into center field. Then Pomeranz began using his curveball.

He ended up throwing 23 fastballs (90 to 93 mph), 25 curves and just enough cut fastballs (eight) to make it a legitimate mix.

“He has confidence in all his weapons,” Farrell said.

In the fourth, though, Pomeranz’s first pitch was an 89-mph fastball that Gregorius lined to left, but it landed in the glove of a diving Andrew Benintendi.

Chase Headley stepped up, and Pomeranz threw two pitches for balls – an 87 mph fastball and a curveball that sailed outside and to the backstop. Second baseman Eduardo Nunez jogged in to check on Pomeranz, then first baseman Hanley Ramirez joined them. Soon, Farrell and the trainer were out of the dugout.

After a chat on the mound, Pomeranz threw a warmup pitch, then headed toward the dugout.

This isn’t the first time Pomeranz has left a game this year because of an injury.

On March 19, Pomeranz left a spring training start because of tightness in his left triceps muscle. He made his next start five days later.

On May 14, the triceps muscle tightened again and Pomeranz lasted only three innings. Still, he made his next scheduled start.

The Red Sox need Pomeranz to come back. Did Boston fans think they would ever be saying those words? After Dave Dombrowski traded prized pitching prospect Anderson Espinoza to San Diego for Pomeranz last year, there was angst. It did not help that Pomeranz had a 4.59 ERA in his 14 games with Boston.

It didn’t get better when Pomeranz’s ERA was 5.29 in mid-May. But now he’s on a roll. The hope is that his early exit Friday was a cautionary move.

Boston is suddenly having bullpen issues, and David Price may not come back this season. Pomeranz’s health is a priority.

Kevin Thomas can be reached at 791-6411 or:

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Twitter: ClearTheBases