Djokovic through to the last eight despite injury problems

Novak Djokovic continued his bid for a record 25th Grand Slam title in style as he stormed past qualifier Jan-Lennard Struff to reach the US Open quarter-finals

‎Despite twice receiving medical attention, the Serb rarely looked troubled as he raced to a dominant 6-3 6-3 6-2 victory in under two hours.

While the win was further evidence of Djokovic's pedigree, questions still remain over the 38-year-old's physical condition.

Djokovic is playing his first tournament since losing in the Wimbledon semi-finals in July, having skipped ATP Masters events in Toronto and Cincinnati.

He looked fatigued in his opening two matches in New York, while he struggled with a lower back injury in his third-round win over Britain's Cameron Norrie.

Again, there were signs of wear and tear as he called for the physio to treat a neck issue and then a problem with his right forearm against German Struff.

However, the setbacks did not appear to harm his tennis as he dictated play with relentless hitting - firing 33 winners and 12 aces, with no double faults.

The world number seven highlighted his serve for keeping him out of trouble on Arthur Ashe Stadium.

Djokovic will face American home hope Taylor Fritz in the last eight after the fourth seed claimed a commanding straight-set win over Czech Tomas