Tennys Sandgren had never won a Grand Slam match or beaten a top 10 player until last week.

Now he's into the Australian Open quarterfinals on debut after adding an upset win over No. 5-seeded Dominic Thiem on Monday night to his earlier victory over 2014 champion Stan Wawrinka.

The 26-year-old American, who entered the season's opening major ranked 97th, missed a match point in the fourth set but held on for a 6-2, 4-6, 7-6 (4), 6-7 (7), 6-3 win over Thiem.

"I don't know if this is a dream or not — all you guys are here, so maybe it's not," he said in an on-court TV interview after his 3-hour, 54-minute fourth-round win. "I'm not in my underwear, so maybe it's not a dream."

Sandgren is only the second man in 20 years to reach the quarterfinals on his debut at Melbourne Park.

He converted half of his eight break-point chances, and fended off 10 of the 12 he faced against Thiem, and hit 63 winners against 38 unforced errors in the biggest win of his life.

"Trying to keep riding the wave," said Sandgren, who was named after his great-grandfather and who comes from Tennessee.

Next up he could meet six-time Australian Open champion Novak Djokovic, who was playing Hyeon Chung in his fourth-round match on Rod Laver Arena.

Defending champion Roger Federer had no real difficulties in reaching the Australian Open quarterfinals for the 14th time, accounting for Marton Fucsovics 6-4, 7-6 (3), 6-2.

The 19-time major winner had never played Fucsovics but had beaten his coach — Attila Savolt — here in the second round in 2002.

Federer will renew a lengthy rivalry next against Tomas Berdych, who returned to the quarterfinals for the seventh time at Melbourne Park with a 6-1, 6-4, 6-4 win over Fabio Fognini.

Federer leads their career head-to-heads 19-6, including all four times they've met in Melbourne and in the Wimbledon semifinals last year.

"We have had some good ones over the years going back all the way to the Olympic Games in Athens in 2004," said Federer, recalling Berdych's comeback win in their first meeting.

The win over Fucsovics was Federer's first day match of the 2018 tournament, and he joked about needing sunglasses and a towel for the beach but said really the only change was to set the alarm for a different time.

Angelique Kerber, the only Grand Slam singles winner remaining in the women's draw, was up earlier, and got a serious wakeup call.

For a while it appeared Kerber's progression could unravel against No. 88 Hsieh Su-wei, a former top-ranked doubles player with a double-handed grip on both sides, until she regained momentum for a 4-6, 7-5, 6-1 win. That earned Kerber a quarterfinal spot against U.S. Open finalist Madison Keys.

With a mix of slice and chips, lobs and bunts, whippy half-volleys and wristy crosscourt ground strokes off both wings, Hsieh pushed Kerber to the extremes.

"Credit to her. She played an unbelievable match," said Kerber, who won the Australian and U.S. Open titles in 2016 and is on a 13-match winning streak to start 2018. "I was feeling I was running everywhere."

Keys returned to the quarterfinals here for the first time in three years with a 6-3, 6-2 win over No. 8-seeded Caroline Garcia, and is yet to drop a set so far.

Top-seeded Simona Halep has had her troubles in Melbourne, including first-round exits in 2016 and '17 and having to rally from triple match point down to advance through the third round this time.

The two-time French Open finalist, who is also contending with a left ankle injury, beat Naomi Osaka 6-3, 6-2 to return to reach the quarterfinals here for the third time.

Hsieh, contesting the fourth round in a major for the first time in a decade, certainly made the most of her time back in the spotlight.

The Taiwanese player took out one major winner — Wimbledon champion Garbine Muguruza — in the second round, and took the first set of Kerber.

Kerber needed to produce her best tennis. She finished 14-shot rally early in the second set by racing forward and reaching at full stretch to track down a drop shot and send a forehand winner over the net post.

After converting a break-point chance with a sliding forehand winner down the line late in the second set, Kerber crouched and screamed to celebrate the point and regaining the momentum.

"I like to play freestyle," Hsieh, a two-time Grand Slam doubles titlist, explaining her unusual array of shots. "Like today I go on the court, if I don't have a plan then I do whatever I can."