0619 GMT February 25, 2020
Earlier in the day, defending champion Novak Djokovic swept past Diego Schwartzman and into quarterfinal with big-serving Milos Raonic as he zeroes in on an eighth Melbourne Park title, AFP reported.
The Swiss master took time to work out the Hungarian but when he did it was one-way traffic, romping to a 4-6, 6-1, 6-2, 6-2 victory to edge closer to a seventh Melbourne title and 21st Grand Slam crown.
"It was a tough start, Marton played very clean," said Federer, who is into his 15th Melbourne quarterfinal, surpassing John Newcombe's 14.
It will be also be his 57th appearance in the last eight at Grand Slams. No one else is close, with Novak Djokovic next in line on 46.
"It just took me some time, I tried to mix it up a bit and just had to figure it out. From the beginning of the second set it got a little bit easier," he added.
Federer, who could face Djokovic in the semi-finals if he gets past Sandgren, wrapped it up in 2hrs 11mins, almost two hours less than his third-round epic against John Millman.
The second-seed Djokovic was on another level to Schwartzman, the 14th seed, crushing the Argentine 6-3, 6-4, 6-4 on Rod Laver Arena to book an 11th appearance in the tournament's last eight.
Raonic is his next hurdle and the Canadian has also been in fine touch. He is yet to drop a set, blasting past fellow former world number three Marin Cilic 6-4, 6-3, 7-5.
"Milos is one of the tallest, strongest players on tour and has one of the biggest serves," said Djokovic.
"I've got to be ready for missiles coming from his side of the net. One key element will be how well I'm returning."
The Serb has met 32nd seed Raonic nine times and won them all.
But the Canadian is back to full fitness after years of injury struggles and his powerful serve could cause problems. So far he has served 59 games and won them all.
Asked what he needs to do to beat Djokovic, he replied, "I think I'm going to have to hit more than 35 aces," referring to the number he pumped past 2018 finalist Cilic.
"I think we play quite opposite from each other, and he's done a good job in the past neutralizing my serve," he added of the Serb.
"So I have really got to focus on my things well and be the one dictating."
Exit in tears
Coco Gauff warned she is not even close to achieving her full potential and targeted the Tokyo Olympics after the 15-year-old exited the Australian Open in tears on Sunday.
Gauff's fellow American Sofia Kenin recovered from a set down to win 6-7 (5/7), 6-3, 6-0 and reach the last eight in Melbourne.
The 14th seed plays Ons Jabeur after the unseeded Tunisian defeated China's Wang Qiang to become the first Arab woman to reach a Grand Slam quarterfinal.
Gauff, the youngest player in the draw, is one of the stories of the Australian Open, beating Venus Williams in the first round and then reigning champion Naomi Osaka in round three.
Gauff, who turns 16 in March and now has to get back to school homework, blamed her loss on too many errors and said that nerves had nothing to do with it.
But she also admitted that the last few weeks had almost been too good to be true.
"I couldn't really write this, I don't think anybody could really write how this past couple months have gone," said the teenager.
"I still have so much I feel like I can get better on. Even my parents, my team, they all believe I can get better.
"I don't even think this is close to a peak for me, even though I'm doing well right now."
The French Open is the next Slam in her sights as she bids to become the youngest player to win a Grand Slam in the Open Era, which began in 1968.
The current record-holder is Martina Hingis, who triumphed at the 1997 Australian Open at 16 years and nearly four months old.