Karolina Pliskova

The sixth seed was tied at 5-5 in the deciding set with her Greek opponent when her smash was called out by a line judge.

Replays showed the ball landed inside the sideline but umpire Marta Mrozinska refused to accept Pliskova's pleadings to overturn the call.

Sakkari won the game and then served out the match to win 3-6 6-3 7-5. Pliskova did not shake Mrozinska's hand and instead smashed her racket several times against the side of the umpire's chair, breaking the wood.

The Czech world No 1, who reached the final in New York last year, required three sets to defeat American home favourite Nicole Gibbs in the second round and was on the brink of defeat before rallying to record a hard fought 3-6 7-5 6-4 success.

Pliskova lost the first set after struggling to gain rhythm in her service games and despite securing an early break in the second set against the Chinese 27th seed she needed to fire a forehand winner down the line to save a match point in the tenth game of the second set with Zhang serving for the match.

Kerber, the top seed, cruised past Japanese qualifier Risa Ozaki 6-2 6-2 while Czech second seed Pliskova beat 15th-seeded compatriot Barbora Strycova 6-1 6-4.

Kerber was barely tested in her 62-minute match during which she displayed a great arsenal of shots and was all over her opponents' serve.

She moves on to face the winner of Monday's round-of-16 clash between Venus Williams and Russian seventh seed Svetlana Kuznetsova.

Angelique Kerber secured her second grand-slam title with a three-set win over Karolina Pliskova in the US Open final.