'We saw it against Rafa, we saw it last night again against Edmund, he brings the power, he brings basically everything, ' he said after beating Chung.
He put the foot down and careered to five set points before taking the tiebreaker with an audacious drop shot.
Meanwhile, Marin Cilic of Croatia advanced to his first Aussie Open final by defeating Kyle Edmund of the U.K.in their semifinal on Thursday. "May be because I stole the first set from him, he felt dejected", Federer joked. "I definitely think I have taken a lot of steps in the right direction and feel good about my game and feel like I'm thinking a lot clearer out there".
"I find it disappointing when some of their breakthroughs come at 27, because then we know them for seven years, let's say".
"You couldn't tell until the end", he said of Chung's injury problems.
Chung, 21, followed up his fourth-round upset of six-time victor Novak Djokovic by downing Sandgren in straight sets.
Federer and Chung all set to begin their semi-final Melbourne.
Federer was cruising 6-1 5-2 when Chung, who was unable to muster much resistance throughout Friday's semi-final, called it a day.
Roger Federer got cranky at the chair umpire for a technology flaw in his Australian Open quarterfinal match, using the rare emotional outburst as motivation.
The South Korean player had taken a medical timeout earlier in the second set to receive treatment on his foot.
But the defending champion was not happy the way the match ended.
Ominously, Federer added: "I'm just pleased that actually my game has been good from the very beginning of the tournament so far".
To beat (Novak Djokovic) here is one of the tough things to do in our sport. "I just knew that I had to restart, actually, after three games - just to stop missing that much and to move better". Federer is likely to play aggressively and try to wrap up the match as fast as possible, while Chung will try to outlast his opponent. "I never playing in second week in Grand Slam, so I'm really surprised", Chung said.
That time-out briefly rallied Chung, in just his 17th major match, to win the next game but he was soon forced to yield to Federer, who was making his 382nd Grand Slam outing.
Sunday's match will be a repeat of last summer's Wimbledon final - when coincidentally Cilic was in tears because of blisters.
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