Unseeded Youzhny had 10 aces in the match that lasted 2 hours, 39 minutes and will face the winner of Saturday's other semifinal between French compatriots Jo-Wilfried Tsonga and Gael Monfils.
Youzhny broke Hewitt in the final game when the eighth-seeded Australian hit two successive backhands into the net.
It was Youzhny's first win over Hewitt in four matches.
Sunday's final will be Youzhny's second of the year. He reached the final of the BMW Open in Munich in May, losing to Tomas Berdych of the Czech Republic. The Russian's last singles title came at Chennai, India at the start of 2008.
Top-ranked Roger Federer pulled out of the $1.2 million event, citing fatigue, along with third-ranked Andy Murray of Britain, who withdrew because of a wrist injury.