Nationals starter Tom Milone delivers a pitch against the Mets in his major league debut. (Greg Fiume/GETTY IMAGES)

The Washington Nationals discovered Tom Milone by accident. On April 4, 2008, Mike Rizzo and Kris Kline, then the franchise’s top two scouts, went to UCLA to watch a right-handed pitcher named Tim Murphy, the same big-time prospect everyone else in the crowded scouts’ section wanted to see. The other pitcher, a skinny left-hander from Southern California, kept stealing their attention.

Milone did not throw his fastball even 90 mph, but he allowed one run and struck out 14. Rizzo pointed at Milone, turned to Kline and said: “That’s our 10th-round pick. He’s gonna pitch in the big leagues.”

That June, the Nationals picked him in the 10th round. Saturday night, Milone arrived in the big leagues. For a while, before Ryan Zimmerman’s two-run, walk-off single lifted the Nationals to an 8-7 victory over the New York Mets at Nationals Park, he felt like he was in a dream. After facing six hitters, all of whom he retired, Milone hit a three-run home run on the first pitch he saw in the majors. Two innings into his career, he walked up the home dugout steps and took a curtain call.

“When I was running down the first base line, it was almost like I was dreaming,” Milone said. “It was almost like I didn’t feel it.”

Zimmerman provided an exultant conclusion with the 14th walk-off hit of his career. The Nationals put runners on second and third with one out in the ninth after a single by Jesus Flores, a walk by Jonny Gomes and a sacrifice bunt by Ian Desmond. Zimmerman stood on deck — and Mets Manager Terry Collins chose to pitch to him, calling for an intentional walk of Roger Bernadina to set up the double play.

“It’s just amazing,” Zimmerman said. “It seems like I always find myself in that position.”

With the count 2-1, Mets reliever Bobby Parnell fired a 100-mph fastball. Zimmerman tried to loft a sacrifice fly and shattered his bat. Right fielder Lucas Duda dove but the ball fell in and two runs scored — a sawed-off walk-off.

Said Zimmerman, “That was luck.”

“I’m kind of surprised it was just a bloop single,” Manager Davey Johnson said. “I was looking for a rocket. But I’ll take it.”

In addition to preventing a 10th loss in 11 games, the win stood as an accomplishment for Milone, 24, and Nationals scouts. Murphy, taken by the Texas Rangers in the third round, has not pitched above Class AA. Milone became the 13th player picked in the 10th round or later in 2008 to play in the majors.

“When the later drafted guys get there,” said Kline, now the Nationals’ scouting director, “it’s even more rewarding.”

Milone’s magical introduction to the majors didn’t last all night. He allowed four runs, all in fourth inning, on six hits. Johnson pulled him with one out in the fifth. The 34,821 fans in attendance gave him a warm ovation, nothing to rival the frenzy after he became the first National since baseball returned to Washington to homer in his first major league at-bat.

Milone arrived after an utterly dominant season at Class AAA Syracuse, showing the same devastating change-up, ability to read swings and knack for keeping hitters off-balance Rizzo and Kline saw that night at UCLA. In 148 innings this year, Milone struck out 155 batters and walked 16 despite topping out at 90 mph with his fastball. He even hit .346.

In the second inning, Milone came to the plate with two runners on base. Mets starter Dillon Gee threw an inside, belt-high fastball. Milone unleashed a quick swing, and the stadium exploded. He sprinted out of the box, then started jogging as the ball soared over the right field fence. He had become the eighth pitcher in big league history to homer on the first pitch he faced.

Nationals relievers jumped up and down as the ball flew over their heads and hit the back wall of the bullpen. Milone cracked a smile, then quickly concealed it, as he rounded third base.

“It was just surreal,” Milone said. “I was hoping for a fastball first pitch. I got it.”

Once he walked into the dugout and sat on the bench, his teammates yelled him to walk to the top stop. Milone, having forgotten a hat or a helmet to tip, raised his right hand in the air. Ivan Rodriguez patted Milone on the head.

“I don’t even know what I was thinking,” Milone said. “It was just such a good feeling. My adrenaline was pumping twice as hard as it was when I was out there pitching.”

Even in his debut, Milone kept a cool demeanor. He threw his fastball inside to right-handed batters without fear. He struck out two and walked none. When Jose Reyes lunged at an 80-mph for strike three, he spun out of the batter’s box to keep from falling over.

“There’s certain players that have the fortitude to kind of rise up to the occasion,” Desmond said. “He didn’t seem shaken or bothered by anything out there. He looked as comfortable as he would have in A ball.”

Milone hit a snag in the fourth. The Mets drilled four hits against him, the last a two-run homer to left by Nick Evans that cut the lead to 5-4.

Milone retired the first batter he faced in the fifth on a flyball. After Reyes lined a single to center, Milone remained in the game and tried to pick him off twice. Then Johnson lifted him for Tom Gorzelanny in order to prevent Milone from taking the loss.

“In some situations, adrenaline kind of took over and I wasn’t able to make as quality pitches as I would hope for,” Milone said. “I was definitely able to make some pitches that I needed to.”

Milone will have another chance five days from now. It would be hard to imagine a fitting encore, something to follow a curtain call on his first night in the majors.

“That was a pretty cool moment,” Zimmerman said. “It’s one I’ll never forget.”