A heartwarming development unfolded in the ninth inning of a tie game.

Edwin Diaz took the mound, struck out the side on 14 pitches, and walked off the field, though his focus would remain on the rubber.

Reds righty Alexis Diaz replaced Edwin and was a bit less dominant, hitting Francisco Alvarez, but escaped unscathed and sent the game into extra innings.

The brothers from Naguabo, Puerto Rico, pitched in the same game for the first time ever, according to Edwin, who is two years older and thus did not overlap much with his little brother growing up.

Their parents, grandmother and sister, among many other family members, were inside Citi Field to see Diaz history — and to see both pitch well, neither costing his team the game.

It made for a touching moment.

But the bigger-picture development for the Mets is that their closer is yet again untouchable.

Edwin Diaz, who has been up and down in his first season back since tearing his patellar tendon, is pitching like the best closer in the game that he was in 2022.

He destroyed the heart of the Reds’ order, primarily with a fastball that has hit triple digits in back-to-back games, and has come up large in the largest portion of the season.

Since that brutal blown save Aug. 29 in Arizona, Diaz has faced 16 batters and struck out 12.

In five scoreless innings spread over nine days, he has walked one and allowed no hits.

There are many positive signs popping up in the Mets’ bullpen — Reed Garrett and Jose Butto were excellent on this night, too, allowing the Mets a chance to walk off the Reds, 6-4, in 10 innings — but the best sign has been that 2024 Edwin Diaz has looked an awful lot like 2022 Edwin Diaz.

“That’s what really good closers do,” manager Carlos Mendoza said after Diaz shook off the grand slam to Corbin Carroll and emerged the next night to begin his most dominant stretch of the year. “Short memory and their ability to turn the page. And Diaz, if not the best, he’s right there with the best.”

Diaz does not quite have the best velocity — that honor belongs to the A’s Mason Miller — but he has among the best when right.

Earlier this season, there were concerns when his heater was living in the mid-to-upper 90s.

On Wednesday, he pounded a 100.8 mph four-seamer that was his hardest of the year. On Friday, despite the heavy usage of late, he touched 100.2 mph.

What’s the difference in, say, Diaz throwing 97 mph and 100 mph?

“A lot,” Mendoza said of Diaz, who put away Elly De La Cruz, Tyler Stephenson and Spencer Steer. “When it’s not 97 and it’s 100, it’s a pretty tough at-bat. It’s a pretty tough pitch to hit.”

Diaz said he knew he had a bit more juice in his arm for when he needed it.

In September, it’s time to unleash it.

“He knows where we’re at in the calendar and what every inning means,” Mendoza said. “There’s that extra gear there.”

It is nice for the Mets that he can reach back for a bit extra, able to buzzsaw just about any hitter when he is at his best.

It is nice for Diaz that he can reach back and hold the lineup card from the day’s game, which he said he would keep because he wants to treasure this memory.

“This is really special,” Diaz said. “We come from a little hometown. To share the field for the first time and both play in the same game — I pitched, he pitched — that’s really fun.”