(AFP) - Roger Federer said that he did not want to lose in front of his young family as he was pushed all the way for the second match in a row at the Shanghai Masters on Thursday.

The reigning champion squeezed into the quarter-finals after eventually defeating the 28th-ranked Spaniard Roberto Bautista Agut 6-3, 2-6, 6-4.

The top seed will play Japan s eighth seed Kei Nishikori, while Novak Djokovic and Alexander Zverev are also through, albeit with far less hassle.

The 37-year-old Swiss great was forced to fight in his opening match on Wednesday against Russia s Daniil Medvedev.

Normal order appeared to have been restored when the 20-time Grand Slam champion comfortably claimed the first set against Bautista Agut.

But the Spaniard earned a piece of personal history after that, winning the second set -- the first time he had taken a set against the Swiss maestro.

The 30-year-old Bautista Agut had the whiff of an upset in his nostrils and the prospect of a first victory over the Swiss at the eighth attempt.

But in the ninth game of the deciding set, Federer made the breakthrough on his opponent s serve, pumping his fist as another hard-won victory loomed into view.

Federer s wife Mirka and their four children were in the arena and he said afterwards: "I m not sure if they give me more courage fighting on court, but they were here today.

"I was telling myself, particularly tonight I cannot do this (lose) because they were there, but I don t know how much I draw from that, quite honestly."

Federer said that two stern encounters had set him up nicely for Nishikori on Friday.

"I hope it s going to help me that I played against Medvedev and also Bautista Agut, two really good baseliners.

"From that standpoint, I feel like I found a rhythm."

One player who will not be in the quarter-finals is Juan Martin del Potro after he hobbled out of the tournament.

The Argentine world number four, who had already been suffering with a virus, lost his footing at 5-5 in the first set against Croatia s Borna Coric.

The 30-year-old Del Potro had lengthy treatment and strapping put on his knee, but conceded the match after losing the first set 7-5.

Coric, the 13th seed, faces Australia s unseeded Matthew Ebden next

Second seed Djokovic enjoyed a measure of revenge as he booked his spot in the quarter-finals with a 6-4, 6-0 demolition of Marco Cecchinato.

The Serbian was stunned by the Italian -- ranked 72 in the world at the time -- in the French Open quarter-finals earlier this year.

It was part of a wretched run of form Djokovic suffered after elbow surgery in February.

But he exploded back to life mid-season, winning Wimbledon, the Cincinnati Masters and US Open.

The 31-year-old says he is back close to the kind of blistering form that has brought him 14 Grand Slams.

Djokovic will play South Africa s seventh seed Kevin Anderson and said he was arrowing in on Rafael Nadal s top ranking. The Spaniard is not in Shanghai due to injury.

"Obviously, I m going to try to do everything I can to get to number one," said Djokovic.

"That s one of the -- probably the -- biggest goal of the end of the season."

Rising star Zverev was similarly emphatic as he brushed aside Australian teenager Alex de Minaur, 6-1, 6-4.

The German fourth seed will next play 11th seed Kyle Edmund.