BEIJING • Rafael Nadal said he has braced himself for the "huge" serve of John Isner, after the world No. 1 bulldozed his way into the China Open quarter-finals yesterday.
The Spaniard, a 16-time Grand Slam champion, saw off Russian Karen Khachanov 6-3, 6-3 to book a last-eight clash with Isner.
The in-form American, seeded sixth, is renowned for his booming service game, and Nadal expects to face a barrage today.
Isner was impressive in blasting his way past Argentina's Leonardo Mayer 6-0, 6-3 and Nadal said: "Tomorrow will be tough against Isner, he's playing unbelievably well.
"He played so aggressive, having a lot of success, hitting a lot of winners, returning very well.
"Everybody knows that he serves huge and it is so difficult to break him. But if you add that he is playing very well now from the baseline, he is one of the toughest opponents you can meet."
Nadal, 31, the top seed who is coming off a third US Open title, saved two match points against Frenchman Lucas Pouille in his opener.
But he was always in control against Khachanov, 21, breaking him in the fourth game of the first set on the way to a routine victory.
In the women's draw, former world No. 1 and fourth seed Karolina Pliskova became the latest high-profile casualty, going out in the third round to unseeded Sorana Cirstea.
Cirstea follows fellow Romanian Simona Halep into the quarter-finals after the second seed sent Russia's Maria Sharapova packing on Wednesday.
Cirstea, ranked 44th in the world, stunned Czech Pliskova 6-1, 7-5 to reach the last eight.
She will play Latvia's Jelena Ostapenko, the Roland Garros champion, after China's top player Peng Shuai retired with a knee injury at 3-0 down in the first set.
The 31-year-old Peng said she had been having injections to ease the pain and her knee was heavily strapped, but she could not play on.
"The doctor suggested I get it treated, but I can only rest after the season, that's the plan," said Peng, ranked 25th in the world.
World No. 1 Garbine Muguruza and reigning champion Agnieszka Radwanska are both out, leaving world No. 2 Halep as the favourite.
Also into the quarter-finals are Caroline Garcia, who defeated French compatriot Alize Cornet 6-2, 6-1, and Czech Barbora Strycova, who beat Daria Gavrilova of Australia 6-0, 6-4 .
Garcia is in red-hot form after winning the Wuhan Open title on Saturday and has a chance of taking the final WTA Finals spot, which starts in Singapore on Oct 22.
She is currently in 10th place and winning the China Open will help her overtake eighth-placed Briton Johanna Konta, going into the penultimate week of the season.
Ukraine's Elina Svitolina, who has already qualified, beat Russian Elena Vesnina 6-2, 7-5 to also enter the quarter-finals. Vesnina needed to win the tournament to stay in contention to reach the WTA Finals.
ATP q-finals: StarHub Ch201, 12.30pm & 7.30pm
WTA q-finals: Ch203, 12.30pm & 9pm