Sinner needed everything in his arsenal to beat the defending champion in a rematch of their Indian Wells semi final and delivered with more than two dozen winners to set up a meeting with Russian Daniil Medvedev in the final.
Up a break in the first set, the 10th seed brought the crowd to its feet when he survived an extraordinary 25-shot rally in the seventh game, sending Alcaraz flailing to the ground with a sensational backhand winner, but handed Alcaraz a break point minutes later.
They traded breaks in the final two games of the set and Alcaraz closed the tie break with an ace. But the Spaniard could not hang onto the momentum and he ceded Sinner a break point with a wild shot out of bounds in the opening game of the second set.
Alcaraz broke Sinner on the third try in the fourth game but was scathed in the effort, landing hard on his left hand, and later met with a trainer at his bench.
The incident took its toll as Sinner broke Alcaraz to love in the ninth game, ending the U.S. Open champion's 21-set unbeaten streak.
Alcaraz returned from a lengthy break in the locker room depleted and he suffered through leg cramps that left him shuffling around the court early in the third set.
Sinner converted on a break point chance in the opening game and Alcaraz was left wincing as he suffered another fall onto his left hand while diving for a serve in the sixth game.
Sinner converted on another break point in the penultimate game and thrust his fists to the air triumphantly after clinching it with a forehand winner.
He will next face Medvedev, who survived a stern test from his friend and fellow Russian Karen Khachanov 7-6(5) 3-6 6-3 for a tour-leading 28th victory this season earlier on Friday.
ONE OF THE BEST OF HIS CAREER
For Sinner, Friday's victory came as an act of revenge after he lost to Alcaraz two weeks ago.
"For sure it's one of the best wins. Obviously, it was a very tough match. I think we both played a very, very high-level match," Sinner told reporters.
"In the third set, I saw him struggling. I tried to push there, especially the first game, because I knew it's the last game that he was serving with the used ball, so it's a little bit easier to return.
"I think I changed a couple of things from Indian Wells to here, which I had to, and they went my way. So I'm happy about that."
Sinner is now aiming for his first Masters 1000 title. but he has yet to beat Medvedev in five meetings, their most recent match coming in the Rotterdam final in February.
"Different conditions (here) than in Rotterdam. I'm very happy that I can face him in a final again," Sinner said.
"The last one I lost obviously, but I'll try my best, I'll try to make some good changes like today against Carlos and let's see. I feel good on this court."
Alcaraz missed the chance to become the first player to win the "Sunshine Double" since Roger Federer in 2017 but the 19-year-old was happy to experience the "beautiful" rivalry with Sinner once again.
"I feel something different about the crowd when I play against Jannik. I think around the world is probably all the people watching this match because I think it's really beautiful to watch," Alcaraz said.
"I had an opportunity to get the Sunshine Double, but I think I'm going to have more years to try to get it. But all I can think about is to improve my level to beat Jannik."
KVITOVA THROUGH
Twice Wimbledon champion Kvitova of the Czech Republic overcame an unruly fan and a first-set deficit to beat Romanian Sorana Cirstea (32), reaching the hardcourt final for the first time in her 13th appearance in Miami.
After a routine start to the affair, a supporter for Cirstea cheered loudly as Kvitova made an error and again in between her first and second serves in the sixth game, a violation of spectator etiquette that saw him reprimanded by an usher.
Visibly rattled, Kvitova ceded the break point to her opponent and needed to summon her veteran calm to turn things around.
"When I was down, I was just trying to put a return in and I played a good return," she told the Tennis Channel. "One fan screaming against me... I know he supported Sorana but you know it wasn't really nice and I got distracted."
With the distraction behind her, Kvitova broke Cirstea in the ninth and 11th games and once again to open the second set, where she upped her level across the board.
She faces last year's Wimbledon winner Rybakina of Kazakhstan in Saturday's final, after beating her in Adelaide in January. Rybakina, the 10th seed, is hoping to keep the good times rolling after winning last month at Indian Wells.
