WASHINGTON — An argumentative Nick Kyrgios hammered 24 aces in a dominating service display to defeat Gilles Simon 6-4, 7-6(5) in the second round of the Citi Open in Washington on Wednesday.

The 24-year-old Australian offered his critique of the chair umpire's performance prior to match point and continued to provide his thoughts following the conclusion of the match on a hot and humid night in the US capital.

Kyrgios will next face Yoshihito Nishioka, a 6-7(5), 6-2, 7-6(5) winner over seventh-seeded David Goffin, under the lights on Thursday.

Top-seeded Stefanos Tsitsipas was tested in his first match of the tournament by Tommy Paul but held on to dispatch the American 6-3, 7-5.

The 20-year-old Greek praised the 22-year-old Paul's performance after their entertaining first career meeting on Wednesday.

"He played very aggressive tennis and was more unpredictable than players I have faced in the past," he said.

"He didn't give me much room to execute my game but I got through it by finding different solutions. I executed my game in a different way."

Canadian teenager Felix Auger-Aliassime topped big-serving American Reilly Opelka to reach the round of 16 in his first main draw appearance at the tournament thanks to his stout defense.

The road gets no easier for the 18-year-old sensation as he next faces imposing sixth-seed Marin Cilic.

Rising Australian Jordan Thompson, top-ranked American John Isner and hard-hitting Canadian Milos Raonic also won their second-round matches on Wednesday.

On the women's side Kristina Mladenovic held on to defeat 17-year-old American Hailey Baptiste 6-4, 4-6, 6-3 in a hard-fought evening match to punch her ticket to the third round.

Baptiste had more power than Mladenovic but the Frenchwoman was the better player in the match's biggest points, converting four of her nine break point opportunities while saving seven of her own.

Russia's Anna Kalinskaya and Americans Lauren Davis and Jessica Pegula also advanced on Wednesday. — Reuters