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Spanish world number one Rafael Nadal has reached the China Open quarter-finals with victory over Russian Karen Khachanov.

Nadal, who won his third US Open title last month, triumphed 6-3 6-3 in Beijing.

The 31-year-old broke Khachanov, ranked 42 in the world, in the fourth game and looked in total control thereafter.

He will face big-serving American John Isner next, who beat Argentina's Leonardo Mayer 6-0 6-3.

Nadal had survived two match points in his opening clash against Frenchman Lucas Pouille, and saved all six of the break points he faced against Khachanov.

His 21-year-old opponent served seven double faults as Nadal registered his 58th victory of the year.

Elsewhere, 19-year-old Andrey Rublev fought back to beat 20th-ranked Tomas Berdych 1-6 6-4 6-1.

Rublev trailed by a set and a break before winning 11 of the next 13 games to level the match, before dominating the Wimbledon semi-finalist in the third set.

The Russian, who reached the semi-finals of the US Open this year, won 64% of points in the third set to register his third victory over a top 20 player, and set up a quarter-final meeting with Alexander Zverev.

Second seed Zverev - who is third in the - beat Italy's Fabio Fognini 6-4 6-2.