Japan's number four Go Soeda beat a top-100 player for the first time in 2015, ousting Alexandr Dolgopolov at the Atlanta Open.
Go Soeda snared his biggest scalp of 2015, downing Alexandr Dolgopolov at the Atlanta Open on Monday.
Soeda had won just three ATP World Tour-level matches this season - the most recent against retiring veteran Lleyton Hewitt in April - coming into his clash with Dolgopolov, but earned a hard-fought 5-7 7-6 (7-5) 6-3 victory.
Dolgopolov, ranked 74th, is without a tour-level title since his Citi Open win in 2012 - and he will now head to Washington hoping to recall his form at the tournament three years ago.
Soeda, meanwhile, advances to a second-round date with fourth seed Adrian Mannarino - who comes into the ATP 250 hard-court event after finishing as runner-up at the Claro Open Colombia in Bogota.
Seventh seed Gilles Muller, finalist in Atlanta in 2012, eased to a 6-2 6-1 win over fellow left-hander, American Donald Young.
Awaiting Muller in the second round is the winner of an all-qualifier match-up between Somdev Devvarman and Jared Donaldson.
Lu Yen-hsun will face second seed Vasek Pospisil in the second round, after the Taipei number one got past Malek Jaziri 6-1 7-6 (14-12).
Jaziri, of Tunisia, served for the second set at 5-4 - but was broken to love.
World number 76 Lu saved six set points in the tie-break, and advanced on his third match point.