BEIJING. Rafael Nadal kept alive his hopes of wresting the top ranking from Novak Djokovic by rallying for a 2-6, 6-4, 6-1 win over Fabio Fognini of Italy in the quarterfinals of the China Open on Friday.Nadal, who needs to reach the final here to have a chance of displacing Djokovic, was down a set and a break but changed the tempo of the match with a timely service break.‘’I was able to fight, to change a little bit the dynamic of the match,’’ Nadal said. ‘’The players who are in the top position of the rankings, it’s because they are able to win when things are not going well. One of the most important things in tennis (is to) win when you don’t play well.’’Djokovic, the defending champion, played Sam Querrey in a late match.In women’s play, top-ranked Serena Williams beat former No. 1 Caroline Wozniacki 6-1, 6-4 to raise her career record to 6-1 against the Dane.Nadal seemed to struggle at times with a niggling left knee injury, but wore down Fognini after that hard-fought service break in the seventh game of the second set.Fognini again ran up a 3-0 lead in the second set and was serving with a lead of 4-2 before Nadal seized control.It was the third straight victory over Fognini for Nadal, who next plays fourth-seeded Tomas Berdych of the Czech Republic. Berdych beat John Isner 7-5, 6-2.In the women’s draw, former Wimbledon champion Petra Kvitova beat local favorite Li Na 4-6, 6-2, 6-4 to set up a semifinal with Jelena Jankovic.Jankovic also came from a set down to beat Lucie Safarova of the Czech Republic 6-7 (3), 6-4, 6-4.