Third seed Alcaraz was far from his usually brilliant self early in his contest but took full advantage of Australian Open champion Sinner's hand cramps to draw level, before sealing the see-sawing match in a decider after a little over four hours.
Having already captured a Wimbledon and US Open trophy at the age of 21, Spaniard Alcaraz became the youngest man to reach Grand Slam finals on all three of the sport's surfaces and will look to emulate several compatriots by winning Roland Garros.
"I have a special feeling for this tournament, because I remember when I finished school I'm running to my home just to put the TV on and watch the matches here in the French Open," Alcaraz told reporters.
"Of course, Rafa Nadal dominated this tournament for 14-15 years. It's unbelievable. I wanted to put my name on that list of the Spanish players who won this tournament... (Juan Carlos) Ferrero, (Carlos) Moya, (Albert) Costa, legends of our sport.
"If I want to be one of the best players in the world, I have to be a good player in every surface, like Roger (Federer) did, Novak (Djokovic), Rafa, (Andy) Murray. The best players have had success on every surface."
Fourth seed Zverev, competing in his fourth straight semi-final in Paris, finally broke the barrier to become the second German man to reach the Roland Garros title clash in the Open Era and match Michael Stich's feat from 1996.
He also banished painful memories of a serious ankle injury in the 2022 semi-final against Nadal, while coming through tough matches this year.
"To go deep and to win a Grand Slam, you have to go through difficulties and you have to go through a lot of ups and downs," said Zverev, who won the match after Ruud was hampered by a stomach issue.
"You're not going to win a Grand Slam by winning every match in straight three sets. Some players do, like Roger, Rafa a few times, but normally to win a Grand Slam you have to go through battles. You have to come back in tough five-set matches.
"You have to come back from difficult moments... I'm happy to be in a Grand Slam final and give myself the best chance to win on Sunday."
Zverev's win came on a day he agreed a settlement after the mother of his child accused him of physical abuse and a German court closed the case.
Ruud rued the fact that his stomach issue had derailed him in what promised to be thrilling clash.
"It's not something I think is very serious or going to last for a long time, but something that came up in the first set...," he said.
"Then the last three went quick because Zverev played well, but I wasn't able to play the kind of tennis I like to play with intensity, because I was limited with my stomach."
Defeat by Alcaraz was a blow for Sinner, who will rise to number one in the world for the first time on Monday but the 22-year-old looked forward to continuing their rivalry although it is not yet at the level of Federer, Nadal and Djokovic.
"Well, you cannot compare us yet with the other players we had or still have," said Sinner, who trails Alcaraz 4-5 after their latest meeting.
"If we see the results... when we play against (each other), it's in the semis or final or quarters. Very important matches.
"I think that's exciting for the game, especially when the head-to-head is quite close. The winner is happy and the loser tries to find a way to beat him the next time.
"That's exciting. That's what I'll try to do."
