Melbourne - South Africa's Kevin Anderson was upset by unseeded American Frances Tiafoe in the Australian Open second round on Wednesday.
The 20-year-old Tiafoe, who is ranked 39th on the ATP Tour rankings, shocked the fifth-seeded Anderson 4-6, 6-4, 6-4, 7-5.
Anderson had gone into the match holding a 3-0 head-to-head advantage against Tiafoe and was looking good leading by a set and 3-0 before his game started to unravel.
Anderson hit 50 winners but made an uncharacteristic 35 unforced errors.
Meanwhile, South Africa's other participant in the men's singles, Lloyd Harris, suffered a heavy defeat at the hands of Russia's Daniil Medvedev in the first round on Tuesday.
The 21-year-old Harris, who qualified for the main draw, was beaten 6-1, 6-2, 6-1 by the 15th-seeded Russian.
In the men's doubles, South Africa's Raven Klaasen and his New Zealand doubles partner Michael Venus opened their campaign with a 4-6, 6-4, 6-3 win against American Bradley Klahn and Kazakhstan's Mikhail Kukushkin.
Klaasen and Venus are the sixth seeds.