BEIJING - Rafael Nadal's bid to return to the top of the world rankings remained on course Wednesday as he progressed to the quarter-finals of the China Open, overcoming stubborn resistance from Philipp Kohlschreiber.
The current world number two could return to the top spot for the first time since July 2011 if he reaches the final in Beijing, and he moved a step closer following his 6-4, 7-6(7/3) victory.
But his German opponent ensured the second seed Spaniard had to dig deep to ensure his passage to the last eight in a game that lasted 1 hour 55 minutes.
Nadal took an early 2-0 lead before being pegged back at 3-3. But he took the first set by breaking Kohlschreiber's serve in the final game.
The intense competition continued into the second set, where neither opponent broke serve, forcing the tie-break.
Nadal paid tribute to his opponent after the match.
"He played great. I didn't serve bad, but his return was amazing," he told reporters.
"When you have a player in front of you that has decided to play completely aggressive, and the balls are going with the right directions, it's very difficult to stop."
Nadal could unseat Novak Djokovic from the top spot, no matter what the Serb does in the competition.
He will face Fabio Fognini in the quarter-finals, after the Italian ruthlessly swept aside Australia's former world number one Lleyton Hewitt in a crushing 6-0, 6-2 defeat.
Elsewhere in the men's tournament, eighth-seed American John Isner beat Spaniard Roberto Bautista Agut 6-2, 6-7, 6-4.
In the women's tournament, Li Na's bid to claim her first major tournament on home soil remained on course as she progressed to the quarter-finals after defeating Wimbledon finalist Sabine Lisicki.
The home crowd favourite dumped out her German opponent 7-5, 6-4 in a cool-headed display of efficiency at a packed National Tennis Centre in Beijing.
The world number five drew loud applause within the first five minutes after she broke Lisicki's serve with the first game of the match.
Lisicki broke back to level the scores at 5-5, but Li powered ahead and took the decisive final two games, with her coach Carlos Rodriguez signalling at her from the stands to maintain her mental strength.
A Mexican wave began as Li won the set. When she broke Lisicki's serve on the fifth game of the second set, the result never looked in doubt as the 2011 French Open winner closed in on victory.
Li said she was satisfied to have maintained her composure when having to score valuable points at the end of each set.
"I was very glad to see that no matter how the score went on the court, I can stay calm and control the match," she told reporters after the match.
In the quarter-finals the fourth seed will face Czech Petra Kvitova, who defeated Italian Sara Errani 6-4, 6-7(7/3), 6-3 in their third-round match.
World number four Agnieszka Radwanska had earlier powered through to the third round with a convincing victory over American teenager Madison Keys.
The Polish third seed took one hour and 15 minutes to claim a 6-3, 6-2 victory over the 18-year-old, who is being tipped as one of the rising stars of women's tennis.
Radwanska, a previous winner in Beijing in 2011, had defeated Keys at Wimbledon in the summer.
Elsewhere, Andrea Petkovic continued her stunning form at the tournament by dumping out former Roland Garros winner Svetlana Kuznetsova 4-6, 6-4, 6-1 in her second-round match.
The German, who is ranked 43 in the world, took just over two hours to claim victory over the 25th-ranked Russian, a previous winner in Beijing in 2006 and 2009.
Petkovic's victory over the 2009 French Open singles champion follows her stunning first-round defeat of second seed and current Beijing champion Victoria Azarenka.
The 26-year-old said claiming the scalps of both the Belarusian -- who won the Australian Open for the second time earlier this year -- and Kuznetsova had given her confidence a massive boost.
"For me, just personally, it's really important to see that I can still beat the players on the top level, two past Grand Slam champions," she said.
"It's just a big boost for my confidence, no matter what happens now in the future."
Elsewhere, eighth seed Jelena Jankovic of Serbia booked her place in the last 16 with a 6-3, 5-7, 6-3 victory over Kazakhstan's Galina Voskoboeva, and Slovenia's Polona Hercog defeated 14th seed Ana Ivanovic of Serbia 6-4, 6-4.
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