Steve Johnson's title defence at the Hall of Fame Tennis Championships came to an end in a surprise first-round loss on Tuesday.
Johnson, the fifth seed at the ATP 250 event, went down to wildcard Christopher Eubanks 7-6 (11-9) 7-6 (7-5) on the grass at Newport.
Eubanks, the 23-year-old ranked 188th in the world, sent down 15 aces in a shock victory over his fellow American.
Defending champion Johnson was one of two seeds to fall, with Bradley Klahn also departing, suffering a 6-4 7-6 (7-5) loss to Denis Kudla.
Alexander Bublik almost joined them in exiting, but the seventh seed edged past qualifier Alex Bolt 6-4 2-6 7-6 (7-4).
Runners-up from the past two years, Ramkumar Ramanathan and Matthew Ebden moved through.
Last year's finalist and a qualifier in 2019, Ramanathan overcame Sergiy Stakhovsky 5-7 7-6 (8-6) 6-2, while 2017 runner-up Ebden claimed a 6-1 2-6 6-3 victory over Brayden Schnur.
Viktor Troicki served 10 double faults but still got past Jason Jung 3-6 7-5 7-5, while Mischa Zverev was too good for Tim Smyczek 6-3 7-6 (7-4).