Andy Murray and Kevin Anderson were the high-profile losers at the Citi Open on Wednesday, while Feliciano Lopez and John Isner won through.
Six seeds - including Andy Murray - were second-round losers at the Citi Open on Wednesday, as the top section of the Washington draw opened up.
Top seed Murray lost a tumultuous clash with world number 53 Teymuraz Gabashvili 6-4 4-6 7-6 (7-4).
It was Murray's first match since Wimbledon, and one the Scot will rue losing - having had the balls on his racquet at 5-4 up in the third set and playing a hampered Gabashvili, who had treatment on a lower left-leg injury.
Gabashvili will play Ricardas Berankis for a spot in the quarter-finals, after the latter ousted 14th seed Pablo Cuevas 6-3 6-3.
The top section of the other half of the draw will also see two non-seeded opponents go head-to-head after fifth seed Kevin Anderson and 10th seed Ivo Karlovic were handed early exits.
Anderson was upended by prodigy Alexander Zverev 2-6 6-3 6-4, while Karlovic was bundled out by Alexandr Dolgopolov 6-4 7-6 (7-2).
Sam Groth saw off ninth seed Viktor Troicki 6-3 6-4, and would have been bound for a clash with Davis Cup team-mate Lleyton Hewitt, except seventh seed Feliciano Lopez staved off the Australian veteran 4-6 7-5 6-3.
Eleventh seed Bernard Tomic lost his way against Steve Johnson, who double-faulted to hand the Australian the first set before correcting himself to earn a 6-7 (7-9) 6-4 6-2 victory.
Escaping the seed carnage were Lopez, Grigor Dimitrov (6), John Isner (8) and Leonardo Mayer (16).
Dimitrov got past qualifier Guido Pella 7-6 (7-1) 6-4, Isner set up a clash with Vasek Pospisil after defeating Victor Estrella Burgos 6-3 7-6 (7-5), and Mayer saw off Blaz Rola 7-6 (7-2) 6-7 (3-7) 6-4.
Fourth seed Richard Gasquet opened his tournament with a hard-fought 5-7 6-4 6-4 win over Gilles Muller - and the Frenchman will face 15th seed Jack Sock for a spot in the last eight.