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.
More to follow.