Australia’s remaining representatives in the joint ATP/WTA China Open have been knocked out in the second round.

French fifth seed Richard Gasquet defeated Bernard Tomic 7-6 (7-2) 6-4, winning with a stunning ace to set up a quarter-final against David Ferrer after the Spaniard overcame Marinko Matosevic 5-7 6-1 6-2.

Novak Djokovic denied being distracted by the threat of losing his number one ranking after he edged through to the quarter-finals on Thursday despite a “lack of concentration”.

The top seed in Beijing remained on course to reclaim the title he won last year after he defeated Fernando Verdasco 7-5 2-6 6-2, while women’s top-ranked player Serena Williams also made it into the last eight.

The Serb’s status as the world number one men’s player is under attack from the second seed in Beijing, Rafael Nadal, who has already made it to the last eight, and only needs to reach the final to claim the top spot.

Djokovic took the first set of his second-round match with relative ease, but his unbeaten run in Beijing stretching back to 2009 looked to be in danger when his Spanish opponent took the second set 6-2.

“I had some chances in the start of the second set and I managed to allow him to come back to the match and start playing well,” Djokovic told reporters, adding that it was a “lack of concentration from my side”.

But he denied that the threat from Nadal was distracting him.

“I try to do what I need to do and that is to win the matches,” he said.

“The rankings will change. They change all the time. Over the years that has been the case. You can’t think too much about it.

“Your job is to win as many matches as possible and the ranking will follow the results that you make.”

The 26-year-old regained his composure in the third set, breaking Verdasco at the first attempt to race to a 3-0 lead, before breaking him again in the final game.

Djokovic, who followed up wins in 2009 and 2010 with victory over Jo-Wilfried Tsonga in last year’s final, faces Sam Querrey in the next round.

The American dumped out the tournament’s sixth seed Stanislas Warwinka 6-3 7-6 (7-2) in their second-round match at Beijing’s National Tennis Centre.

In the women’s tournament, world number one Serena Williams claimed victory over Maria Kirilenko in two unconvincing sets, with the scores finishing 7-5 7-5.

The top seed was forced to summon extra strength at the end of each of her two sets as her Russian opponent became increasingly aggressive.

Kirilenko was poised to claim the first set at 40-0 up with the score at 5-4 in her favour, but after missing three set points, Williams stepped up a gear to overturn the scoreline.

The American was also forced to come from behind in the second set, with Kirilenko, a former winner in Beijing in 2005, leading 4-3. But Williams then broke Kirilenko’s serve before closing in on victory in the third-round match.

In the quarter-finals, Williams will play Danish number six seed Caroline Wozniacki who beat Sloane Stephens 6-3 6-1.

She appeared to be uncomfortable at times on the court, but said she had no injuries.

“I have little aches everywhere, but I’m feeling okay,” Williams said.

Czech Lucie Safarova ended Andrea Petkovic’s fairytale China Open with a hard-fought 6-4 6-7 (7-4) 7-6 (7-2) victory.

The German had dumped out previous Beijing champions Svetlana Kuznetsova and Victoria Azarenka in the opening rounds.

Polish third seed Agnieszka Radwanska powered through her third-round match, with a ruthless 6-0 6-2 victory over Slovenian Polona Hercog.

Seventh seed Angelique Kerber and eighth seed Jelena Jankovic also safety negotiated passages through to the last eight.

Kerber, Germany’s top ranked player, defeated Italy’s Roberta Vinci 6-2 6-4, while Jancovic disposed of Spaniard Carla Suarez Navarro in her third-round match, with the Serb taking both sets 6-0 6-0.