French Open 2013: Novak Djokovic driven on in pursuit of title as a tribute to his former coach At 77 years old, she must have known that her breast cancer was becoming increasingly serious, yet she said that she was in hospital for a routine check-up. Djokovic's chief rivals will no doubt be supportive and sympathetic. As Ernests Gulbis complained last week, the leading players are unfailingly polite to each other. Yet they must also be groaning at the idea of the world No 1 on an emotional crusade. He is good enough without an extra cause to fight for. That, however, is exactly how Djokovic is now looking at this tournament. "I feel even more responsible to go all the way," he said last night. I want to do it for her, because she was a very special person in my life. If Djokovic is to deliver on his promises, he has three more matches to win at this tournament after beating Germany's Philipp Kohlschreiber on Monday. He never quite found his most irresistible form, dropping the first set on a cold and windy afternoon, but even so Kohlscreiber never threatened an upset. Djokovic will next play Tommy Haas, who yesterday became the oldest man - at 35 - to reach the quarter-finals here since 1971. As for Rafael Nadal, he had a stroke of luck when his next opponent, Stan Wawrinka, was pushed to the very limit in an extraordinary five-set match with Richard Gasquet. Despite hitting a mind-boggling 92 winners, Wawrinka had to fight all the way to 8-6 in the decider. He spent four hours 16 minutes on the court, which is not going to help the thigh injury he has had for a few weeks. Yet the level of his play has been spectacular this year, even going back to the moment when he served for the match against Djokovic in the fourth round of the Australian Open. Wawrinka-Nadal has the makings of a classic, because Nadal looked to be finding his way back to form yesterday in a 6-4, 6-1, 6-3 eviction of Kei Nishikori. At two hours two minutes, it was comfortably his shortest match of this French Open and came on his 27th birthday. "Seriously, if you told me two days ago you will play like this today, I will say, "Give me the paper and I will sign,"" Nadal said, "because I'm happy the way I improved my game. My feeling was today when I was hitting my forehand that I wasn't going to miss the ball. First few days, I don't know if the ball is going to go inside or outside. I started to feel that I can hit the ball longer and have more confidence in every stroke. In the women's tournament, it was a day of frustration for the Americans, who had arguably over-performed by making up four of the last 16 players. Bethanie Mattek-Sands, Jamie Hampton and Sloane Stephens all lost in straight sets, the latter 6-4, 6-3 to defending champion Maria Sharapova. At least Serena Williams, who faces Svetlana Kuznetsova in the quarter-finals, is still going strong for the United States.