Jacob deGrom keeps it 100 (mph) in return, but Mets get worrying updates on Noah Syndergaard, J.D. Davis

Jacob deGrom returned to the mound on Tuesday night and threw a 100-mile per hour fastball with his first pitch.

The Mets exhaled.

But news from Florida about Noah Syndergaard made the Mets hold their breath again.

Syndergaard left a rehab start for Class A St. Lucie after one inning because of right elbow soreness.

The Mets said he was removed for “precautionary reasons,” as if that was enough to stem the tide of worrying that will follow about a pitcher who is coming back from Tommy John elbow surgery.

There were no further details about Syndergaard’s condition or whether he was going to need any medical tests.

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It was Syndergaard’s second rehab start. He was supposed to go four innings. In the inning he did pitch, the righthander walked one and struck out one against the Daytona Tortugas.

A scout at Syndergaard’s truncated outing said via text: “He was 94-95 first few batters. 89-92 to the last couple.”

More bad injury news: J.D Davis, who was rehabbing a sprained left hand with Triple-A Syracuse and then developed a stiff neck, has returned to New York for “treatment,” according to a source. It was not immediately clear for which ailment.

Meanwhile, back at Citi Field, deGrom made his first start since May 9 — he had been on the injured list with a sore right side — and looked very deGrom-like in an all-fastball, eight-pitch first inning.

That 100-mph opening pitch was chopped to short by Raimel Tapia for the first out. The rest of the inning went like this: 100, 99, 99, 100, 101, 101 and 100, the last two producing outs (Trevor Story fly ball to right on 3-and-2, Charlie Blackmon grounder to James McCann at first).

After the Mets took a 1-0 lead on McCann’s RBI groundout, deGrom picked up his first strikeout against C.J. Cron leading off the second. But Ryan McMahon tied the game with a homer to left-center on a 100-mph fastball.

The next batter, Brendan Rodgers, grounded a single to right that beat the shift. Garrett Hampson lined out to right and deGrom struck out Dom Nunez to end the inning.

DeGrom, who came into the game batting .467 (7-for-15), took two healthy cuts in his first at-bat in the bottom of the second and struck out on a 2-and-2 pitch.

There had been speculation the Mets would not let deGrom swing the bat, as they did with Taijuan Walker earlier this month when he was pitching with an injury. But deGrom took his hacks.

DeGrom struck out the first two batters of the third inning on six pitches before Story hit a first-pitch grounder to third.

DeGrom struck out two in a 1-2-3 fourth.

DeGrom came in with an 0.68 ERA and had struck out 65 in 40 innings and walked seven. He had struck out 46.1% of the batters he faced.

DeGrom made one rehab start for St. Lucie. He struck out eight of 10 batters over three hitless innings and hit 102 mph with his fastball.

The Mets, as you might expect, were happy to have him back.

“It’s great. It’s great,” manager Luis Rojas said. “It’s a good sign because everyone in there knows that there’s a group of [injured] guys who’s going to be coming in order, all at their different times. No rush, right now, as far as for them to go through the progression to [get back] with us. To get Jake today, I know it’s huge for everyone. We feel that the guys are coming back, but we’re talking about the best pitcher in the game, right? So yes, definitely uplifting. Awesome that he’s starting for us . . . Lost a start or two. But he’s back.”

With Tim Healey

Anthony Rieber covers baseball, as well as the NFL, NBA and NHL, for the sports department. He has worked at Newsday since Aug. 31, 1998, and has been in his current position since July 5, 2004.