Baseball, maybe more than ever, is a young man’s game. Consider the wave that crashed ashore Tuesday night at the All-Star Game. Bryce Harper, 20, of the Washington Nationals, became the youngest position player to start an all-star game since Ken Griffey in 1990. Manny Machado will need an exemption to rent a car for another four years, but he robbed a hit Tuesday night with a breathtaking throw across the diamond. Mike Trout, another 21-year-old, led off the game with a double against some oldster named Matt Harvey, who despite his advanced age of 24, managed two scoreless, dominating innings before a frothing Citi Field crowd.

And then they all stopped to watch an old man. In the eighth inning of the American League’s 3-0 victory, Mariano Rivera walked through the bullpen gates. “Enter Sandman” rumbled from speakers. The field behind him remained empty. The top step of both dugouts brimmed with the best baseball players on the planet, whom the placid 43-year-old on the mound had turned into awestruck little boys.

“He’s one of the best pitchers in the history of the game, to be honest with you,” Cardinals right-hander Adam Wainwright said. “I don’t think there’s ever been a better pitch in baseball than his cutter. He’s thrown one pitch his entire career. Teach me that pitch. I would love to do that.”

Forty-five players made either their first or second all-star team Tuesday night. Rivera, baseball’s all-time saves leader, pitched in his 13th and last Midsummer Classic. The respect for him throughout baseball is unmatched, but he is still making the showcase on merit — this year, he has a 1.83 ERA and 30 saves.

It was all a surprise to Rivera, he would say later. He didn’t know that no teammates would join him on the field during his warmup, leaving him alone on the stage. He didn’t know he would pitch the eighth — AL Manager Jim Leyland did not want to take the chance of the NL erasing a lead against another reliever and then the game ending before Rivera could pitch. He didn’t know he would be named MVP, the first pitcher to win the honor since Pedro Martinez in 1999.

On the mound, Rivera removed his New York Yankees cap, kissed it and lifted it over his head, turning to acknowledge every corner of the standing ovation. Rivera threw his first warmup pitch to catcher Salvador Perez, a 23-year-old Kansas City Royal who was 5 when Rivera made his debut. Only then did the defenders trot to their positions behind Rivera.

“We wanted to give him his due,” Leyland said.

Goosebumps remained as Rivera finished his warmup. He carved through another 1-2-3 inning. Brewers shortstop Jean Segura, 23, came to bat first and grounded out. “He only throws one pitch,” Segura said. “Everybody knows it’s that pitch coming.”

Cardinals first baseman Allen Craig, 28, had never previously faced Rivera. He had watched Rivera since he was a kid, and he always wondered what it would be like to see Rivera’s cutter from the batter’s box. On the on-deck circle, he had joined the standing ovation.

“I was kind of thinking to myself, ‘Man, this is one of those special moments that I see on TV growing up, that people will never forget,’ ” Craig said. “And then I found myself on deck, a part of it. It’s just a cool deal.”

Craig lined out to left. Brewers outfielder Carlos Gomez chopped to short, ending the inning. Rivera threw 16 pitches. They were all cutters.

“His legacy is that he’s the best closer to ever play,” Wainwright said. “The cutter is just the legend within the legacy. It’s like a fairytale pitch.”

Rivera is the pitcher everyone will remember, but every other American League hurler who pitched provided a show, too. The AL held the NL to only three hits, singles from Carlos Beltran in the fourth and David Wright in the seventh and a double by Paul Goldschmidt in the ninth.

Harper, the only Nationals player in the game, went 0 for 2 with a sharp lineout and a flare to shortstop, facing White Sox left-hander Chris Sale and Oakland A’s closer Grant Balfour. Harper patrolled center field for four innings and switched to right field for two more.

National League Manager Bruce Bochy kept Harper in the game long enough for him to take two at-bats, and the NL’s meager offense meant Harper played longer than any player except Wright, the hometown idol and NL captain.

After Max Scherzer and Sale tore through the first eight NL batters, Harper came to bat with two outs and the bases empty in the third against Sale, one of the toughest lefties in baseball.

Sale started Harper with two lethal sliders, and Harper laid off both. He looked at a 95-mph fastball and then fouled away a 2-1 slider. Sale fired another 95-mph heater. Harper smoked it toward the opposite field, but in the precise direction of Miguel Cabrera’s glove. The ball bored into Cabrera’s mitt before Harper had a chance to leave the batter’s box.

“I was just was trying to lay off the slider,” Harper said. “I knew I couldn’t hit it.”

On defense, Harper ran down and caught everything in his direction. Last year in his first all-star appearance, while playing left field, he lost a ball in the Kansas City dusk. He had no such problem at Citi Field, ranging to left-center and cutting in front of Colorado Rockies left fielder Carlos Gonzalez to make one catch.

Harper was very much a part of the theme of this year’s game. On Monday afternoon, one of baseball’s fresh stars had identified a unifying characteristic.

“We all play fearless,” Trout said.

In perhaps the perfect statement about the young talent pouring into baseball, Trout led off the game against Harvey. The right-hander zipped a 97-mph fastball. Trout lashed a grounder down the first base line and into the right field corner for a leadoff double.

Next came the night’s most harrowing moment. On the second pitch of the at-bat, Harvey yanked a 97-mph fastball and drilled Robinson Cano on the upper leg. Cano walked to first, but after Harvey struck out Cabrera with a wicked slider, Cano limped off the field.

“Obviously, that was the last thing I wanted to do, was go out there and possibly injure someone,” Harvey said.

The worst fears evaporated quickly. Cano had a hamstring contusion and might miss a few games, but he should return in a matter of days.

By the end of the night, Rivera had risen above anything else, a singular figure with a single pitch. He had given all the younger men around him something to aspire to.