Britain's Kyle Edmund sprung another surprise as he beat John Isner of the United States ©Getty Images

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Kyle Edmund proved too strong for big-serving American John Isner ©Getty Images
Kyle Edmund proved too strong for big-serving American John Isner ©Getty Images
John Isner looked good in the opening sets but eventually ran out of steam ©Getty Images
John Isner looked good in the opening sets but eventually ran out of steam ©Getty Images
Novak Djokoic's opponent Mikhail Youzhny withdrew from their contest when trailing 4-2 in the first set ©Getty Images
Novak Djokoic's opponent Mikhail Youzhny withdrew from their contest when trailing 4-2 in the first set ©Getty Images
Novak Djokovic has now benefitted from two consecutive walkovers at the US Open ©Getty Images
Novak Djokovic has now benefitted from two consecutive walkovers at the US Open ©Getty Images
Madison Keys battled back from 5-1 down in the third set to beat Japan's Naomi Osaka ©Getty Images
Madison Keys battled back from 5-1 down in the third set to beat Japan's Naomi Osaka ©Getty Images
The Japanese player was visibly emotional after suffering a tense loss at the hands of Keys ©Getty Images
The Japanese player was visibly emotional after suffering a tense loss at the hands of Keys ©Getty Images
Rafael Nadal of Spain has still yet to drop a set at the tournament ©Getty Images
Rafael Nadal of Spain has still yet to drop a set at the tournament ©Getty Images
Britain's Johanna Konta made light work of Belinda Bencic of Switzerland on her way to round four ©Getty Images
Britain's Johanna Konta made light work of Belinda Bencic of Switzerland on her way to round four ©Getty Images
Marin Cilic, winner of the 2014 US Open, suffered a surprise defeat at the hands of American Jack Sock ©Getty Images
Marin Cilic, winner of the 2014 US Open, suffered a surprise defeat at the hands of American Jack Sock ©Getty Images