The third-seeded Klizan will face fourth-seeded Fabio Fognini of Italy, who beat Daniel Gimeno-Traver of Spain 6-3, 6-4 in the other semifinal.
Youzhny overcame a 5-3 deficit in the first set and saved three set points in the tiebreaker to win it. Klizan then came back from 4-2 down in the second by winning four consecutive games to force a third set.
He broke Youzhny in the sixth game of the decider and led 5-2 but could not score a single point in the next three games and it went to a second tiebreaker. Klizan jumped out to 6-3 and sealed the victory after 3 hours, 49 minutes with a powerful first-return forehand on his first match point.
"I was fighting from the beginning to the end, that's why I think I won," Klizan said. "Because I had a very big motivation and I really wanted to win. I had some problems with my back but still was fighting for each point."
Both players called for the doctor: Youzhny had his right toe plastered while Klizan had his back massaged.
Youzhny, the 2004 champion and a two-time runner-up, said he was lucky in the first tiebreaker while Klizan played better in the second one.
Fognini will play in his second career final after winning his maiden title in Bucharest, Romania in April.
Fognini rallied in the first set by winning four consecutive games, and in the second set made the decisive break in the seventh game. He converted his second match point advancing to the net and making a short, low forehand.
"Semifinal is always a tough match," Fognini said. "If you win you're into the final for sure, if you lose you always go home. My good serve was the key today."Suggest a correction