Murray, Ferrer through to China Open semis

The three-time Grand Slam champion was forced into a tense 20-point tie break in the first set by his 21-year-old compatriot, finally clinching it with a forehand passing shot.

But Edmund -- who upset 18th-ranked Roberto Bautista Agut in the second round -- was unable to hold his serve in the second, conceding the match 7-6 (11/9), 6-2.

Zverev, 19, was looking to cap a breakout season with a second title in Beijing, but was unable to capitalise on his first set lead as he was overpowered by Ferrer 6-7 (4/7), 6-1, 7-5.

The German upset the Swiss world number three Stan Wawrinka to win his maiden ATP title at St. Petersburg in September, having downed number nine Tomas Berdych in the semis.

In Beijing he beat 10th-ranked Austrian Dominic Thiem in the first round, making him the first teenager to defeat three top 10 players in a row since Boris Becker in 1986.

Despite the loss, Zverev -- who started the year ranked 83 -- is expected to rise to 21 when the new rankings are released Monday as he edges towards a place in the top 20 for the first time.

- Olympic rematch -On the women's side, in an Olympic effort Madison Keys overpowered Petra Kvitova in their first meet since the Czech denied the American a bronze medal in Rio.

It took two hours and 40 minutes, three sets and two tie breaks for Keys to exact revenge over the double Wimbledon champion, 6-3, 6-7 (2/7), 7-6 (7/5).

A double fault by Kvitova turned the first set in favour of Keys, but she pulled back in the second pushing it to a tie break, which she won.

There was little between the pair in the final set, but Kvitova's 32 unforced errors to Keys' 25 ultimately cost the Czech a semi-final place -- and ended her eight-match winning streak.

"She made it really tough today. I'm just really happy that at the end I was able to get my serve back on track and get myself ahead in the tiebreaker," Keys told reporters after the match.

Kvitova has had a year of up and downs since she split with her coach of seven years David Kotyza after the Australian Open in January.

She ended last year runner-up in the WTA Finals in Singapore but this season she has failed to get past the round of 16 at any of the Grand Slams, and her ranking fell to 16 -- its lowest since 2011.

Keys, 21, made her top 10 debut this year after winning her second career title in Birmingham in June.

The big hitting youngster -- who is often cast as a successor to 22-Grand Slam champion Serena Williams -- is also chasing her first qualification for the elite WTA Finals in Singapore, which features the season's top eight players.

With her quarter-final win she moves into seventh in the Race to Singapore leaderboard, but Briton Johanna Konta is hot on her heels and she needs to win the title in Beijing to clinch her spot.

Konta plays home favourite Zhang Shuai for a semi-final place later Friday.

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