The 20-time Grand Slam champion was given a warning for swearing during his great escape against Sandgren, when he saved seven match points before winning in five sets to set up a semifinal against seven-time champion Novak Djokovic.
Defending champion Novak Djokovic and Roger Federer will be playing each other for the 50th time when they meet in the semifinals at Melbourne Park.
Third seed Federer went into Friday's match nursing a groin injury exacerbated during his epic quarter-final win against American Tennys Sandgren, and required treatment after a first set against Djokovic which he had seemed on course to win before blowing three break points at 4-1 ahead.
In order for Federer to capture his third Australian Open championship in four years, that skid will need to end Thursday.
The Serbian eventually completed a 7-6 6-4 6-3 win to reach an eighth Australian Open.
But when footage of the women's semi-final showed Federer walking underneath Rod Laver Arena in his match attire, fears were allayed.
So why hasn't Federer managed to win a Grand Slam match against Djokovic in eight years?
Federer headed straight off court for another medical timeout, this one apparently for treatment to his lower back, while Djokovic also consulted the doctor and took a pill.
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That proved pivotal as Federer went on to lose the opening set, allowing Djokovic to seize control from then on.
A similar scoreline was expected here, with Federer going into a match as probably a bigger underdog than any contest since the early stages of his career.
"I think I overall played all right".
"Back in the day I feel like we could speak to linespeople", Federer said.
"Roger is Roger. You know that he's always going to play on such a high level, regardless of the surface", Djokovic said. "I just want to say respect to Roger coming out tonight". "Nice entrance, nice send-off, and in between is one to forget because you know you have a three percent chance to win".
"No idea. Same as a year ago". But look at the end of the day, I'm very happy.
Victory for Djokovic on Sunday would hand him his 17th Grand Slam title.
One positive for Federer is that he does not think the problem will cause him long-term issues.