FEDERER MAKES SHAKY START
With the exception of injured world No 1 Rafael Nadal, Federer's chief rivals are all still in the mix.
Juan Martin del Potro and Alexander Zverev both defied illness to join Federer and Novak Djokovic in the next round.
Del Potro, the third seed, said that he is suffering from a virus and reviewing his health "hour by hour", after labouring past France's Richard Gasquet.
The Argentine lost Sunday's final of the China Open in Beijing to unseeded Nikoloz Basilashvili and afterwards revealed that he had been unwell.
Three days on and the 30 year old continues to be under the weather, but just about did enough to see off Gasquet 7-5, 7-6.
Between coughs at his post-match press conference, Del Potro said, "It wasn't easy to play for me today, I did what I can. I didn't run too much.
"But I'm going like hour by hour and see how I'm feeling," added Del Potro, who plays 13th seed Borna Coric of Croatia next in Shanghai.
"I got lucky that I won, but tomorrow will be a different day.
"If I have a good night today and I have a good recovery tomorrow morning, maybe I will feel a little bit better for tomorrow night and play better than today."
The 21 year old Zverev fought off a cold - he has had a sore throat and blocked nose for a few days - and the raw power of Basilashvili, winning 7-5, 6-4.
The fourth seed will play Australia's world-ranked 33 Alex de Minaur.
Zverev said that Basilashvili, who is up to a career-high ranking of 23, "knows how to play, definitely".
"Probably the hardest-hitting player I have ever played against," said Zverev.