Top-seeded Jessica Pegula reached her eighth WTA quarter-final of the year on Thursday, but the anticipated men's clash between Taylor Fritz and Andy Murray was postponed as rain washed out the night session of the hardcourt tennis tournament in Washington.

Pegula, ranked fourth in the world and the 2019 champion in Washington, defeated lucky loser Peyton Stearns 6-3, 6-4 to set up a mouthwatering quarter-final meeting with Ukrainian Elina Svitolina on what promises to be a busy Friday.

Ukraine's Marta Kostyuk also advanced, toppling women's second seed Carolina Garcia of France 6-2, 6-3.

Men's top seed Fritz and three-time Grand Slam champion Murray were originally scheduled to cap Thursday's action in a fight for an ATP quarter-final berth.

But their match was pushed back a day, as was that between local favorite Frances Tiafoe and Chinese teenager Shang Juncheng.

After several hours of rain, Tiafoe and Shang took the court for what had been scheduled as the opening match of the night session.

They had made the coin toss but were soon ushered off as the rain returned.

Before the showers hit, fifth seed Grigor Dimitrov, France's Ugo Humbert and American J.J. Wolf booked quarter-final berths.

Bulgaria's Dimitrov defeated Emil Ruusuvuori 6-4, 6-3, Humbert raced past Japan's Yosuke Watanuki 6-0, 6-2 and Wolf beat fellow American Michael Mmoh 6-4, 7-6 (7/5).

Dimitrov will face Humbert for a semi-final berth while Wolf awaits either Tallon Griekspoor or Gael Monfils, who had split the first two sets and played one game of the third when rain stopped play.

Jordan Thompson and Christopher Eubanks will also return to finish their interrupted round of 16 match, the winner taking on either Fritz or Murray.

On the women's side, Greece's Maria Sakkari and Canadian Leylah Fernandez had their match postponed until Friday, with the winner earning a quarter-final meeting later in the day with Madison Keys.

bb/sco