Mets prospect A.J. Ewing showed off his blazing speed when he belted an RBI triple in the seventh inning of his major league debut on Tuesday night in Citi Field.

But it was the reaction of his joyous family that stole the show. His dad, Joe, and his other family members were pumping fists, high-fiving and going crazy after Ewing’s big hit in a Mets 10-2 win.

In the second inning, Joe talked to SNY’s Steve Gelbs after the rookie worked the first of his three walks, saying he was built for this moment.

But Joe admitted he was a “nervous wreck watching him.”

Joe, who said he was a high school pitcher who couldn’t hit, did say he was the one who started his son on the path to becoming a left-handed hitter at 3 years old.

Joe, who had six messages on his phone before finding out, was surprised his 21-year-old son was called up so soon.

“He’s definitely grown as a player,” Joe said. “I think when he first realized, ‘Hey, I have a shot to be a major league player,’ he went after that dream really, really hard.”

Joe said others saw more of his son’s potential than he originally did.

“I knew he was good baseball player, but I knew how hard it was to get to this level,” Joe said. “I think being his Dad, I … didn’t think he was as good as he really was, maybe.

“The first time I was having a conversation with an agent talking to me about my son, I remember I looked at him and said, ‘You think my kid is going to get drafted?’

“He stopped and he paused as calm as can be and said, ‘I know you’re kid is going to get drafted.’

“I said, ‘What!’ Then it kind of hit me, ‘Alright, here we go.’ ”

Ewing filled up a lot of the stat box in the win.

Besides becoming the first Met to hit a triple for his first big league hit, he also walked three times, stole a base and had two RBIs.