Sandgren beats Thiem after lobbing stunning accusation

Tennys Sandgren has shocked No.5 seed Dominic Thiem in a five-set thriller to reach the quarter-finals of the Australian Open on Monday, but it wasn't without controversy.

The American held strong in a topsy-turvy match to win 6-2 4-6 7-6 (7-4) 6-7 (7-9) 6-3 in four hours on Hisense Arena.

Sandgren, the world No.97, had never been beyond the first round of a grand slam before this month's tournament.

"I'm starting to disbelieve (his continued success) a little bit," he said after the match.

"I don't know this is a dream or not. All you guys are here so maybe it's not. I'm not in my underway so maybe it's not a dream."

Sandgren will face Hyeon Chung, who he credits with lifting him to his current level following a match earlier in the summer, or No.14 seed Novak Djokovic on Wednesday.

The loss was another blow for the rising star Thiem, who has lost in the fourth round in his past five non-clay majors.

Earlier in the match, Sandgren seemingly made the stunning accusation that a person in Dominic Thiem's player's box has repeatedly clapped during the American's service motion.

Tennys Sandgren blew up. Pic: Channel 7

Tied at one set apiece and the third on serve at 3-2, Sandgren engaged the chair umpire with some furious comments as the controversy erupted.

"I'm right here to serve. That's ridiculous. In a player's box?" he began.

The chair umpire appeared to respond that she did not hear any noises, which frustated Sandgren further.

Dominic Thiem. Pic: Getty

"When I say someone in the crowd's making noise you say 'I don't know'," he said.

"When someone's doing it to directly inhibit me, 'Oh, I don't know. Good luck'. That's pretty cool.

"There's one person clapping in a sea of 2000 people. You have no idea where it came from? Wow. That's a great idea.

"You haven't said anything. Somebody's done something and you've not stopped them from doing it again. That's what I'm saying. There was no repercussions for doing it on a break point, second serve.

"No repercussions. Nothing happened, nothing happened. Why would he not do it again? He got away with it, no repercussions."

The chair umpire appeased Sandgren before the next game when she asked the crowd to remain quiet between serves.