Britain's Kyle Edmund lost his second-round match in three sets to Grigor Dimitrov at the Citi Open in Washington on Wednesday.
The British No 2 went down 7-5 4-6 6-3 to his Bulgarian opponent in two hours and 20 minutes at Rock Creek Park Tennis Center.
Edmund, 22, saved two set points at 5-6 in the opener but Dimitrov took a third to take control of the match inside 56 minutes.
The world No 41 responded well in the second, breaking his opponent in the third game and saving four break points in the sixth before going on to wrap up the set and level the match.
However, Edmund crucially double-faulted in the eighth game of the decider to hand Dimitrov a break point which he accepted - and the Bulgarian served out to book his place in the third round against Daniil Medvedev, who beat Steve Johnson 3-6 6-4 7-6 (7-1).
Qualifier Yuki Bhambri surprised Frenchman Gael Monfils with a shock victory in the capital.
Indian Bhambri, the world No 200, beat sixth seed Monfils 6-3 4-6 7-5. His deserved success, completed in an hour and 50 minutes, earned Bhambri a third round tie against Guido Pella.
Tennys Sandgren progressed after Nick Kyrgios retired when trailing 6-3 3-0 with the Australian departing the court to a chorus of boos.
The American he will next face Alexander Zverev, who came from behind to knock out Jordan Thompson 4-6 6-3 7-5 (7-5).
Elsewhere, Kevin Anderson won 6-4 6-1 against Malek Jaziri to set up a match against top seed Dominic Thiem.
Gilles Miller beat Dimitry Tursunov 6-1 6-2, Jared Donaldson knocked out Marc Polmans 6-2 6-3, while Tommy Paul was another straight-sets winner, beating Lucas Poule 7-6 (8-6) 6-3.
Marcos Baghdatis defeated Ryan Harrison 6-4 6-1 and will next face third seed Milos Raonic, a 7-6 (7-2) 7-6 (10-8) conqueror of Nicolas Mahut.
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