Nishikori marches into Citi Open quarters

Novak Djokovic & Simona Halep celebrate titles at Wimbledon Champions Dinner

Second seed Kei Nishikori booked his spot in the quarter-finals of the Citi Open courtesy of a 6-4, 6-4 victory over Leonardo Mayer.

On a day in which their were a number of seeded casualties, Nishikori and third seed Marin Cilic stood firm to progress as the highest-ranked players in the draw following Andy Murray's early exit on Wednesday.

Nishikori required an hour and 33 minutes to see off the challenge of Mayer, breaking the Argentine once in each set, while never needing to defend a break point opportunity on his own serve.

The opening set of the encounter was interrupted by rain on three occasions, but Nishikori was not distracted from his task, breaking Mayer at 3-3 before going on to serve out the set.

The second set remained on serve until Nishikori raced out to a 0-40 lead in the ninth game, completing the break on his second opportunity.

Nishikori will face Sam Groth in the last eight after the Australian defeated seventh seed Feliciano Lopez 6-3, 6-4, in what will be the first meeting between the pair.

Third seed Marin Cilic required two tiebreakers to down 13th seed Sam Querrey 7-6(2), 7-6(3). Neither man faced a break point in the opening set, but it was Cilic who surged ahead in the tiebreaker, racing out to a 6-1 lead before serving out the set.

Querrey responded strongly to going a set down, breaking Cilic early in the second set, but the US Open champion broke back at 3-5 with Querrey serving for the match. Again it was Cilic who held his nerve in the resulting tiebreak.

The 18-year-old Alexander Zverev, who beat Alexandr Dolgopolov 2-6, 6-2, 6-4.

Sixth seed Grigor Dimitrov saw his charge ended by the unseeded Steve Johnson, the American triumphing 6-3, 1-6, 6-3 in an hour and 32 minutes.

Fourth seed Richard Gasquet joined Dimitrov in heading for the exit, with the Frenchman beat 7-6 (4), 6-7 (5), 6-4 by 15th seed Jack Sock.