The 31-year-old took his winning streak to 14 matches since the start of the US Open where he claimed a 16th Grand Slam title.
Rafael Nadal continued to scythe his way through the Shanghai Masters on Thursday, reaching the quarter-finals with a 6-3, 6-1 thrashing of temperamental Italian Fabio Fognini.
The Spaniard needed two minutes over the hour to dispatch Fognini, taking his winning streak to 14 matches since the start of the US Open where he claimed a 16th Grand Slam title.
The 31-year-old is closing in on finishing the year as world number one for the first time since 2013.
Fognini was playing the day after being handed a suspended ban from two grand slams and $96,000 fine for verbally abusing a female umpire at the U.S. Open.
Roger Federer, who was up against tricky Ukrainian Alexandr Dolgopolov later at the Qi Zhong Centre, is the only player who can stop Nadal sealing the year-end honour for a fourth time.
Former U.S. Open champion Juan Martin del Potro won the match of the day by stopping third seed Alexander Zverev, recovering from losing the opener to win 3-6 7-6(5) 6-4.
Sixth seed Grigor Dimitrov, who saved match points on Wednesday against Ryan Harrison, had a more comfortable day as he beat American 10th seed Sam Querrey 6-3 7-6(3).
Dimitrov, closing in on a first appearance at the ATP World Tour Finals, plays Nadal next.
Wimbledon runner-up Marin Cilic also eased into the quarter-finals with a 7-6(1) 6-4 defeat of American Steve Johnson.
