Melbourne - Tennys Sandgren won a "war" against 12th seed Fabio Fognini over four intense sets to roar into his second Australian Open quarter-final in three years Sunday.
The American proved too hot for the Italian who was nursing a battered hand, winning 7-6 (7/5), 7-5, 6-7 (2/7), 6-4 to set up a last-eight clash against either Roger Federer or Hungarian Marton Fucsovics.
"That was fun. Playing him was just a war," said Sandgren, ranked 100.
"He is so good. You can never count him out at any stage. I had expectations of a fight and that's what we had."
Sandgren, a devout Christian, achieved his best Grand Slam result at Melbourne Park by reaching the last eight in 2018, but it was overshadowed by a row over his political views and links to right-wing activists.
He has put the controversy behind him and shown battling qualities in his run to the quarter-finals this year, having also knocked out eighth seed Matteo Berrettini in the second round.
Asked about playing either Fucsovics or Federer, he said: "Marton is playing phenomenal at the moment and Roger is Roger."
Sandgren's clash with unpredictable firebrand Fognini had plenty of highs and lows.
Nerves began fraying after Sandgren won the first set and Fognini was allowed a toilet break, with the American confronting the umpire.
"He gets his own rules because you're afraid to step on his toes," he ranted.
"If you're wondering why players think you guys give people different treatment, this is one of the reasons why. I think he gets different treatment."
Fognini was then given a point penalty for taking his shirt off, before seeking treatment for his right hand that he injured by punching his racquet earlier in the tournament.
The distractions didn't unsettle Sandgren who went two breaks and 4-0 up in the second set before Fognini came steaming back, winning five games in a row before he was broken again and the American regained focus to go two sets in front.
Sandgren needed treatment for an upper leg problem in the third set, which went to another tie-breaker with the Italian looking fresher as he took it to a fourth set.
There was little between them as they battled for supremacy in some high quality rallies until Fognini blinked first and Sandgren broke to win the match in the 10th game, taking a theatrical bow in front of a boisterous crowd.
Collated results on day seven of the Australian Open Grand Slam at Melbourne Park on Sunday (x denotes seeding):
Milos Raonic (CAN x32) bt Marin Cilic (CRO) 6-4, 6-3, 7-5
Novak Djokovic (SRB x2) bt Diego Schwartzman (ARG x14) 6-3, 6-4, 6-4
Tennys Sandgren (USA) bt Fabio Fognini (ITA x12) 7-6 (7/5), 7-5, 6-7 (2/7), 6-4
Roger Federer (SUI x3) bt Marton Fucsovics (HUN) 4-6, 6-1, 6-2, 6-2
Petra Kvitova (CZE x7) bt Maria Sakkari (GRE x22) 6-7 (4/7), 6-3, 6-2
Sofia Kenin (USA x14) bt Coco Gauff (USA) 6-7 (5/7), 6-3, 6-0
Ons Jabeur (TUN) bt Wang Qiang (CHN x27) 7-6 (7/4), 6-1
Ashleigh Barty (AUS x1) bt Alison Riske (USA x18) 6-3, 1-6, 6-4