A tennis antihero was in the house for Friday’s opening U.S. Open men’s semifinal, but his name was James Scott Connors — Jimmy or Jimbo to you — and not Daniil Medvedev, who played the role of the bad boy in the early rounds of this year’s tournament, but almost immediately turned contrite and decorous on his march through the draw.

As Connors took in Medvedev’s impressive 7-6, 6-4, 6-3 victory over Roger Federer-slayer Grigor Dimitrov, one was reminded of just how civilized society has become over the decades. Baseball beanball wars are obsolete and so are hockey bench-clearing brawls. On the field, on the ice, on the rink, at least, we have evolved.

The way that Connors routinely acted, the way that John McEnroe and Ilie Nastase acted out on the court and verbally abused officials, well, that’s no longer tolerated. You might want to check with Serena Williams on that. No time any longer for anti-heroes on Ashe, even for the guys the paying customers might love to hate.

Which, you know, for a couple of nights early in the fortnight was Medvedev, jeered madly during his second-round match after he snatched a towel from a ball kid, tossed his racket in the direction of the umpire, made a surreptitious obscene gesture and generally acted like a boor, the way Connors and McEnroe and Nastase did as a matter of routine. Medvedev then poked the bear of the crowd that had booed him, and then did it again following his third-round match.

But the 23-year-old Russian was never comfortable wearing the villain’s black hat. He’s a good guy, he is. He wants to be a good guy and he wants you to know that. He was cheered warmly by the audience Friday and basked in the reception. Now he will play for the championship Sunday against Rafael Nadal, who advanced by blasting away Matteo Berrettini 7-6, 6-4, 6-2 after rallying from 0-4 and 4-6 in the tiebreak.

And if Medvedev pulls off the upset, if he stops Nadal from winning his 19th major, which would propel the Spaniard to within one of Federer’s record, you could imagine him receiving the trophy to the cheers of the crowd and turning into Sally Field winning the Oscar, proclaiming, “You like me, you really like me.”

“I will not say that I am a kind person or a good person,” said Medvedev. “I can only say I’m a really calm person in life. I actually have no idea why the demons go out when I play tennis. Especially when I was a junior, I had a lot of problems with my attitude.

“I was working hard because every time I do something wrong on the court, I’m sitting with myself, I’m not like this in normal life. Why does it happen? I don’t want it to happen like this. So I have been working a lot on it and I have improved a lot.”

Medvedev isn’t some schlub. Ranked fifth on the tour and seeded fifth in this tournament, he is 20-2 during the U.S. hardcourt season and has become the third player in the Open Era to reach the finals consecutively in D.C., Canada, Cincinnati (where he won) and Flushing Meadows. Ivan Lendl and Andre Agassi preceded him.

This, of course, was a different-look Grand Slam semifinals, the first with three players (Medvedev, Demitrov, Berrettini) born in the ’90s, and only the fifth in which the 33-year-old Nadal was the only one of the Big Three left standing in the semis. Federer, 38, went down in the quarters while Novak Djokovic, 32, was beaten in the fourth round.

The tennis world is spinning off its axis and whether this event represents a blip or a reckoning remains to be seen. But Nadal has a pretty good idea of where, eventually and inevitably, this is going.

“We have been here for 15 years. At some point, now sooner than later this era is going to end. It’s arriving at the end. The clock won’t stop. That’s part of the cycle of life.”

On Sunday, Nadal will attempt to stop the clock at least momentarily and pay it forward. On the court against Medvedev. Two good guys. Not an antihero in sight, unless you can spot Connors in the crowd or McEnroe in the television booth.