In a sense, it was a strange return to post-trade deadline action for the New York Mets on Friday.

José Buttó and Tyler Rogers were in opposite dugouts. Old friends like Wilmer Flores and Dominic Smith contributed for the Giants. The Mets rallied to erase a 3-0 deficit, but struggled with runners in scoring position at the worst time and took a 4-3 loss.

Brad Penner-Imagn Images

A positive, however, came from one of the Mets’ prime deadline adds: right-handed reliever Ryan Helsley.

Ryne Stanek surrendered a run earlier, but it was otherwise a solid job from the New York bullpen on Friday. The go-ahead run came from the courtesy runner in extra innings against Edwin Díaz, who still hasn’t allowed an earned run since June 2. But right before Díaz’s inning, Helsley kept it tied with a scoreless ninth.

He did allow two hits, but he struck out three as he gave the Mets a chance to walk it off.

Helsley’s first batter as a Met was a three-pitch strikeout on three fastballs with triple-digit velocity. Grant McCray stared at two above the knees, then swung at one up in the zone for strike three.

Helsley used his over-the-top, explosive motion to overpower the young McCray.

He broke out the slider against Patrick Bailey. Left-handed batters came into the game 0-for-27 against that pitch. Bailey chased the first slider Helsley threw at him. But the next one Helsley tried didn’t break, and Bailey lined into center for a single — breaking that pristine streak.

With the right-handed Heliot Ramos batting, Helsley mixed the two pitches. He induced a chase on a slider, then got ahead 1-2 with a fastball called for a strike. He retired Ramos with another swing-and-miss on the slider.

Helsley’s slider is an upper-80s pitch, but it’s deceptive on hitters and has some sharp, late break to it.

He threw nothing but triple-digit fastballs to Rafael Devers, who’d been 0-for-4 with four strikeouts on the night. But Devers fought off a 100.3 mph fastball up in the zone for the Giants’ second hit against Helsley.

That wasn’t much issue for Helsley, who recorded his third strikeout — and second of the three-pitch variety — to strand the go-ahead runs on base. He went with all sliders this time to the right-handed Willy Adames.

Adames swung and missed at a slider right down the middle, then fouled one off. Helsley ended the inning with perhaps his nastiest offering yet, getting Adames to wave at one in the dirt. It was a commanding way to end his first inning in orange and blue.

Batters came into the game hitting just .092 on Helsley’s slider. It’s a pitch he’s thrown more often than his fastball over the past two seasons, and for good reason. Although his fastball can blow hitters away, it’s still a straight offering that can get hit. Coming into the game, the pitch had a .406 opponent batting average against it. Notably, the expected batting average was much lower at .332 — but it’s not ideal. It’s a big part of why Helsley had a human 3.00 ERA with the Cardinals this year.

Opponents hit a more reasonable .276 against Helsley’s fastball last season, when he posted a 2.04 ERA. In each of the last two seasons, he’s thrown his slider around 48% of the time and fastball around 45% of the time. It’s a mix that’s generally worked well for him. And on Friday, he showed just how nasty he can be when he’s at his best. The key for him will just be hitting his spots.

So, despite the loss in the Mets’ first game back from the trade deadline, Helsley gave them something to be excited about in setup opportunities to come.