NEW YORK -- When David Peterson returns from paternity leave next week, he will rejoin a Mets pitching staff that is steadily growing healthier. Max Scherzer is due back on Tuesday. Chris Bassitt will return from the COVID injured list at some point, followed around the All-Star break (or shortly thereafter) by Jacob deGrom. If the Mets succeed in reassembling all those pitchers in their rotation, it could conceivably become difficult for Peterson to retain his spot.

But that line of thinking is surely changing. Upon matching his career high with 10 strikeouts in a 4-3 win over the Rangers on Friday at Citi Field, Peterson improved to 2-0 with a 2.45 ERA in his last three starts. He has struck out 18 batters without a walk over the last two of them, showcasing the type of stuff that prompted the Mets to make him a first-round pick in the 2017 MLB Draft.

Peterson has, in other words, done enough to warrant a rotation spot regardless of which other pitchers might be around him.

“It’s what I expect out of myself,” Peterson said. “I have the confidence that I can contribute. I can compete at a high level here for this team and help us win games.”

The most notable element of Peterson’s performance was his slider, of which he threw 24 in total and 21 in the strike zone. Although Peterson has leaned more on his curveball and changeup this year than in the past, his slider remains by far his most likely pitch to generate swings and misses. So it was Friday, when his seven whiffs with the pitch included swinging strikeouts of Kole Calhoun (three times), Marcus Semien, Adolis García, Leody Taveras and Josh Smith.

“That slider was nasty tonight,” Rangers manager Chris Woodward said. “Guys were getting frustrated because he just wasn’t leaving anything out over the plate. He was burying the right-handed slider in on guys and wiping out the lefties away from it. It was good stuff.”

Peterson credited his ability to throw first-pitch strikes as the catalyst that allowed his slider to be effective as a putaway pitch. Over the past month or so, Peterson has focused on exactly that, trusting his stuff early in counts rather than trying to get hitters to chase. Although Semien and Nathaniel Lowe both hit solo homers on offspeed pitches early in counts, those did not cause much harm because Peterson was so adept at limiting traffic on the bases.

Rangers starter Glenn Otto was the opposite, allowing three baserunners in the fourth before Eduardo Escobar hit a decisive three-run homer.

“First-pitch strikes are vital,” said Peterson, who allowed three runs on five hits over six innings. “And they didn’t seem too eager to jump on the first pitch tonight.”

Peterson, who was on regular rest for Friday’s start, only found out he was making it on Thursday, when the Mets drew up plans to place Bassitt on the COVID IL. Because Peterson had already been scheduled to start on Saturday, the change in schedule did not do much to throw off his routine. But with his wife a full week past her due date back home in Colorado, Peterson was always a bit concerned that he would be called away for the birth before the weekend began.

In that manner, the timing worked out fortuitously for the left-hander, who now plans to work out at Citi Field on Saturday before boarding a flight to Colorado. If all goes as expected, Peterson will be present for the birth, and able to return to the Mets in time to start next week in Cincinnati.

That’s a right he’s earned, given his recent results. As long as Peterson continues delivering in that manner, the looming presences of Scherzer, Bassitt and deGrom shouldn’t affect his rotation spot.

“I feel like I’ve proven myself that I can compete at this level, that I belong here,” Peterson said. “So yeah, when I get the opportunity, I’m going to make the most of it and run with it.”