it was an error-strewn match with gilles simon. giving him a test. >> reporter: novak djokovic looked unstoppable this season, up against a determined gilles simon, the defending champion appeared to meet his match. novak djokovic made 100 unforced errors and was taken all the way to five sets by the frenchman. he's persevered to four hours and 32 minutes before reaching the quarterfinals taking on kei nishikori. no such problems for serena williams, with 21 grand slams to her name, she's three short of a record held by margaret court. as the australian tennis legend watched from the stand. serena williams took a step closer to slam 22. williams was rarely troubled in her straight-sets victory over russia's margarita gasparyan, as she booked her place in quarterfinals, giving her the rest of the day to herself - not quite what nick williams had planned. >> i haven't been doing anything. i've been spending a lot of time worrying about myself this trip. it's kind of sad. i'm alone a lot. i'm kind of like boring. >> reporter: what hav