Al Leiter made the pitch.

And now Eli Manning is throwing fastballs.

It was Leiter who directed Manning to trainer Mickey Brueckner, who has gotten positive results for Red Sox pitcher and former Seton Hall Prep star Rick Porcello and for Leiter’s 97 mph-throwing son Jack, who will be a freshman at Vanderbilt this fall.

“I feel better, I feel stronger,” Manning said.

Leiter is not the least bit surprised.

“What he did, and his commitment to it, will absolutely make him stronger and in better position for the throws that are necessary,” Leiter told The Post. “Bottom line, bottom line: You create the throwing pattern and the strength that goes with it to help maintain and sustain arm speed and strength. If you have the arm speed, I don’t care if you’re throwing a [5.6-ounce] baseball or whatever the hell a football weighs [14-15 ounces].”

Leiter, an ex-Yankee and ex-Met, was once a fireballing left-hander who retired at age 40 with two World Series rings over a 19-year career.

“I kinda imparted my opinion as a guy that’s older than Eli, that was able to play to 40 years old, that it was much more difficult to do the things at 38, 39 than I did at 27,” Leiter said.

Leiter lives across the street from Manning in New Jersey and broached the topic with him in the spring.

“I just gave a relative story to my career, and how life gets harder when you get older and your body’s not the same, so on and so forth,” Leiter said. “And I was inquiring as to what the NFL does with respect to strength and conditioning folks that really hone in specifically on the throwing motion. To my surprise, I think all teams don’t do much of it. There’s a couple of gurus out there but nobody specifically to train the thrower.

“He was all ears.”

Considering Brueckner’s work with Leiter’s son, and out of respect for Manning, Leiter said he didn’t want it to appear as if he were promoting Brueckner.

“If I was the owner of a [NFL] team, I would go find the best throwing-strength conditioning guru guy that knows every aspect of the throwing motion biomechanically and I’d pay him just to work out my quarterback. Period, that’s it,” Leiter said. “So, all these quarterbacks around the country, they look for guys all around the country, they fly out to see like Tom House and all these other people. It’s ridiculous. It blows my mind.”

Brueckner and Manning began working together in January and trained four to five days a week, specifically focusing on bolstering Manning’s arm strength and building back his athleticism.

“The biggest thing with him was he had great flexibility and mobility, his throwing mechanics were on par and there was no issues there whatsoever,” Brueckner told The Post. “From my assessment, he just needed to get stronger and build rotator-cuff strength, stability and strength, and improve rotational power. So, we did a ton of med[icine]-ball throws and things like that. The biggest thing that he had never really done before, was applying a progressive throwing program.”

Each week, Brueckner planned out which days Manning was going to throw, the approach for each session, and how they were going to move forward in building his strength, distance and intensity. It was about a six-week program before the start of OTAs and was dependent on how Manning was feeling.

For Brueckner, building Manning’s explosive power was a priority, gearing sessions toward rapid-force production, getting in and out of cuts and creating general stability. And despite the fact Manning is 38, he gave the same kind of energy Brueckner sees in the younger athletes he trains.

Manning said he’s worked in a baseball environment before and he looked to Brueckner, a former pitcher for Arizona State whose hopes for a professional career were derailed by two Tommy John surgeries, to help with effectively integrating techniques that are used for any overhead-throwing athlete.

“I feel like it has paid off, I’m throwing the ball well. The arm is staying strong, [staying] three or four days after practice to not lose it which is what happens in training camp sometimes,” Manning said. “You have four practices in a row, if you are not used to it, you can see your arm getting tired and it’s still feeling strong and coming out good.”