Novak Djokovic and Roger Federer face tricky quarter-final matches at the Shanghai Masters on Friday after the star pair battled through to the last eight.

World number one and defending champion Djokovic defeated John Isner 7-5 6-3, while second seed Federer got the better of David Goffin, earning a 7-6 (9-7) 6-4 success.

Djokovic goes on to tackle Stefanos Tsitsipas, who overcame a significant scare as he beat Hubert Hurkacz 7-5 3-6 7-6 (7-5), with Alexander Zverev up next for Federer.

German Zverev threatened to blow Andrey Rublev away after a first-set rout, but he was then made to work hard to come through 6-0 7-6 (7-4).

Daniil Medvedev, the third seed, and Dominic Thiem, the fourth seed, both won in straight sets, seeing off Vasek Pospisil and Nikoloz Basilashvili respectively.

DJOKOVIC SERVES UP A TREAT

The top seed was speaking of the threat of Isner's famous serve from the moment their last-16 clash was booked and continued to do so after his win.

But Djokovic also managed to execute his own serve as effectively as he had hoped, complementing his typically excellent defensive game to get through.

"I managed to kind of read his serve and find a good position on the return - at the end of the first set and also the beginning of the second," the Serbian said.

"I won five games in a row and that was the key - obviously having a break each set, and then I held my serve. I thought it was one of the best serving matches I've had lately."

FEDERER FLUSTERED BUT THROUGH

If Djokovic performed better than he might have expected, Federer was a little taken aback by the level of opponent Goffin, whom he thrashed in straight sets for the loss of just four games at the US Open.

"I never really felt like I had the upper hand over David today," Federer said. "I thought he did a really good job. He was so much better than at the US Open."

STILL TWO MINOR UPSETS

The top eight seeds would have made up the quarter-final line-up if not for wins by Italians Fabio Fognini and Matteo Berrettini.

Fognini, the Monte Carlo champion who made headlines for a spat with Andy Murray earlier in the week, defeated Russian Karen Khachanov 6-3 7-5.

Berrettini, who lost to Murray last week, a month on from reaching the US Open semi-finals, got the better of Roberto Bautista Agut, tying up a 7-6 (7-5) 6-4 victory.

Fognini faces Medvedev next, with Berrettini up against Thiem.