The world number one and US Open champion Alcaraz will face his Laver Cup conqueror Taylor Fritz in Tuesday's decider of the Japan Open.

No man since the legendary Rafael Nadal in 2017 has reached 10 finals in a season.

"Following his steps in making 10 finals in a season is something great," said Alcaraz, who also set a new personal best of 66 wins in a season.

"Hopefully it's not going to end here -- a few tournaments ahead, hopefully (I'll) get to the finals there as well."

Alcaraz has wowed the crowds this week but he was in danger of being outshone by Norway's world number 12 Ruud, who pulled off a series of spectacular winners to take the first set.

Alcaraz, who suffered an ankle injury on Thursday in his opener, regained control in the second set before closing out the match with another ferocious display of power-hitting.

"Emotionally it was really tough to deal with everything today," he said.

"I'm really happy to be able to turn around everything and I ended that match playing such great tennis.

"I'm excited to be playing in another final."

His opponent will be world number five Taylor Fritz, who beat the Spanish superstar in San Francisco two weeks ago.

Fritz beat fellow American Jenson Brooksby 6-4, 6-3 in the day's other semi-final.

Alcaraz practiced with Fritz in Tokyo before the tournament began and he described his final opponent as "a really difficult player to play against".

"That practice gave me a really good feedback to how I should approach the match," said Alcaraz.

"I will try to play my best tennis tomorrow -- my Plan A, if I want to beat him -- because his level is pretty high right now."

Alcaraz picked up from where he left off in his quarter-final win over Brandon Nakashima, pounding Ruud with some huge forehands early in the match.

But the Norwegian had a few tricks up his sleeve as well, drawing applause from Alcaraz when he floated a winner to the baseline from a difficult angle.

Ruud took the first set when Alcaraz, beginning to show signs of frustration, hit a return long.

The 22-year-old came back strongly, sending down nine aces in the second set alone to tie up the match.

Alcaraz broke Ruud midway through the third set and never looked back, sealing victory with another jackhammer forehand.

"Physically, it can be better, I'm not going to lie," said Alcaraz, who has been playing with his ankle strapped since his injury.

"Just doing the best work that I can with my team, with my physio, and hopefully tomorrow it will be even better."