(Reuters) - Top seed Novak Djokovic overcame a second set blip to beat Spaniard Fernando Verdasco 7-5 2-6 6-2 and reach the quarter-finals of the China Open on Thursday, keeping alive his hopes of clinging on to his world number one ranking.
The defending champion, aiming for his fourth China Open title in five years after missing the 2011 tournament through injury, will lose the top spot next week if Spaniard Rafa Nadal reaches the final in Beijing.
In the quarter-finals, the Serb will face American Sam Querrey, who caused an upset by defeating sixth-seed Swiss Stanislas Wawrinka 6-3 7-6(2) in 76 minutes.
While much is being made of the No.1 battle the 26-year-old six-times grand slam champion insists winning, rather than ranking points, is his sole focus when he takes to the court.
"I try to do what I need to do, and that is to win the matches," Djokovic told a news conference.
"Rankings will change. They change all the time. Over the years it has been the case. But you can't think too much about it. Your job is to win as many matches as possible and the rankings will follow the results that you make."
The Serb wasted an early break of serve in the first set and had to wait for the final game to break Verdasco again and seal the opener.
Using his forehand to great effect Verdasco fought back, breaking Djokovic's serve twice in the second set to take the Serb into a centre court decider.
Reigning Australian Open champion Djokovic, without a title since the Monte Carlo Masters in April, quickly re-established his superiority to snuff out any chance of a shock.
"(It was a) lack of concentration from my side," Djokovic added. "I had some chances at the start of the second set, and I managed to allow him to come back into the match and start playing well.
"But, again, the important thing is that in the third set I regained the focus and the patience also, decreased the unforced errors, and managed to get a win, which is what counts."
(Reporting by Sudipto Ganguly in Mumbai; editing by Martyn Herman)