Djokovic is now one behind Roger Federer's record of 58 grand slam quarter-finals after a 6-2 7-5 6-4 victory.

The Serbian second seed got himself out of a minor pickle at 2-0 down in the second set, breaking back and dropping just four points in his next six service games.

A break to love in the third finished 6ft 5in Gojo off with Djokovic going through in two hours and 25 minutes.

Djokovic, bidding for a 24th grand slam title, said: "I knew Borna has a big game. I saw that he played well in the qualifying round.

"I saw that he's a big-shot player, his serve and forehand are big weapons, he moves pretty well for a big guy, so the key points for me were to neutralise his serve."

Djokovic has had a very agreeable draw in New York but he faces American ninth seed Taylor Fritz on Tuesday.

He added: "You know, obviously the matches are only going to get tougher from now onwards, and I'm ready."

Big-serving Ben Shelton blew away fellow American Tommy Paul to lead the home charge into the quarter-finals.

The 20-year-old from Atlanta fired down two 149mph serves in one game on his way to a 6-4 6-3 4-6 6-4 victory.

"I think it was straight adrenaline," he said. "In any other atmosphere I don't think I could get it done. I think my arm would fall off, but it's feeling good right now."

The record fastest serve at the US Open is still held by Andy Roddick, who hit a 152mph thunderbolt on his way to the title in 2003 - the last time an American man won their home slam.

It was sweet revenge for Shelton, who was knocked out by Paul at the same stage of the Australian Open in January.

He added: "I really learned how to be mentally tough. When I was playing in Australia after a long week, I was looking at my box saying 'my legs are dead, I'm tired, I can't go anymore'.

"I realised how important it is to believe in myself, believe that I can go all the way, the full distance emotionally and physically and now I have that belief here."

Shelton will play 10th seed Frances Tiafoe, guaranteeing at least one American man in the semi-finals.

Tiafoe beat Australian wild card Rinky Hijikata in straight sets, 6-4 6-1 6-4.

"It's a shame that two of us have to play in the quarter-finals. Maybe we could have three in the semis," added Shelton.

Fritz beat Dominic Stricker of Switzerland in three sets to make the last eight at Flushing Meadows for the first time.

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