Young American Jack Sock claimed the biggest win of his career to eliminate SAP Open winner Milos Raonic from the US National Indoor Tennis Championships in Memphis.
Number two seed Raonic, runner-up in each of the last two years, crashed out at the first round stage after Sock claimed a surprise 6-3 5-7 7-5 win.
"It's always nice to get the highest-ranked win of my career," Sock said. "I hope to carry the momentum on this week."
Tommy Haas and Alexandr Dolgopolov had no such problems on Wednesday.
Sixth-seeded Haas, a runner-up in San Jose last week, defeated Evgeny Donskoy 7-6 (8/6) 6-4, while seventh seed Dolgopolov defeated Bjorn Phau 6-3 6-4.
Former world number one Lleyton Hewitt will join them in the second round after he saved match point on two occasions to edge past Yen-Hsun Lu 2-6 7-6 (7/3) 6-4.
Hewiett's fellow Australian Marinko Matosevic is also through following a 7-6 (8/6) 6-4 success over Japan's Go Soeda.
American Donald Young progressed courtesy of a bye after Xavier Malisse retired injured at 5-1 down in the first set.