Wawrinka - who stunned the three-time defending champion, Novak Djokovic - meets the Czech Tomas Berdych, a man who has one grand slam final to his name but is battling to shed the tag of perennial underachiever.
Federer, who defeated a slightly ring-rusty Andy Murray in four sets to reach the last four, will prepare for his own semi-final against Rafael Nadal by watching Wawrinka and he admits things may get animated.
"I don't sit there all quiet," Federer said. "At the end [of the Djokovic match] I was standing up, hands in the air like him. When he wins big points, I guess you do fist pump. I high-five with Mirka [his wife]."
Wawrinka will doubtless appreciate the support of his compatriot but he will have to conquer the inevitable nerves of trying to reach the final, especially in a match he can win.
Beaten by Djokovic in the semi-finals of the US Open, he should feel more at home on the big stage but Berdych is playing impressively and the stakes are high for both men. "Berdych has been playing well since the beginning of the tournament," said Wawrinka. "He's really close to the top guys."
Berdych lost to Rafael Nadal in his only previous grand slam final, at Wimbledon in 2010, and trails the Swiss 8-5. Berdych remains optimistic, though. "I'm going to give 100%," he said.