Alcaraz will also be seeking revenge in Tuesday's clash in Tokyo after a shock defeat by Fritz at the Laver Cup in San Francisco this month, his first loss to the American in four career meetings.
"He's been playing great tennis lately," Alcaraz said.
"At the Laver Cup against me, against Alexander Zverev and in this tournament ... he's feeling great and really comfortable on the court, so I'll try to change a few things. Obviously the speed of the court and everything is different.
"It's going to be another challenge for me but I'm excited about it and I will try to take the good things I've done today and the good things I did in San Francisco. It's going to be an interesting match."
Six-time Grand Slam champion Alcaraz wasted four chances to break Ruud early and let out screams of frustration when his Norwegian opponent closed in on the first set with sublime shot-making from the back court and at the net.
Having dropped the first set, the Spaniard came out all guns blazing in the next and levelled the scores with a huge ace before turning on the style to break for a 3-2 lead in the decider and secure the win.
"I had a lot of chances in the first set," the 22-year-old said.
"It was really close. It's just about the tennis. A match can change on small details so I tried to be there, tried to be more positive than the first set. I was a little bit mad with myself so I just tried to play with joy again."
American Fritz earlier saw off compatriot Jenson Brooksby 6-3 6-3 after flawless serving in tough moments to reach his third final of the season after claiming grasscourt titles in Stuttgart and Eastbourne.
"I served insanely well today," said 2022 champion Fritz, who pounded 13 aces.
"A high percentage of first serves ... hit a lot of lines. It felt like any game I didn't hit three aces, he was putting a ton of pressure on me, outplaying me from the baseline most of the match."
