Fifth seed Kevin Anderson is out of the Australian Open after being beaten in four sets by American Frances Tiafoe.
Anderson, who reached the final at Wimbledon in 2018, took the first set 6-4 but his 20-year-old opponent fought back to take the next three 6-4 6-4 7-5 and seal a place in the third round.
World number 39 Tiafoe had never previously progressed beyond the second round in Melbourne.
Elsewhere, Marin Cilic beat Mackenzie McDonald 7-5 6-7 (9-11) 6-4 6-4.
The Croatian sixth seed was pushed hard in the early stages of the match but his class eventually showed against the 23-year-old American.
Cilic will now play either Spaniard Fernando Verdasco or Radu Albot of Moldova, while Tiafoe's reward for his shock win is a match against Italy's Andreas Seppi, who earlier beat home favourite Jordan Thompson in straight sets.
"It means the world to me," said Tiafoe, speaking on court after his victory. "I lost to Kevin three times last year.
"I would love to get to the second week of a Slam and if you guys get behind me like you did again, then it's going to be pretty easy for me."
Also through is Greece's Stefanos Tsitsipas, who beat Serb Viktor Troicki 6-3 2-6 6-2 7-5. He plays Georgian Nikoloz Basilashvili next.