Rafael Nadal is taking nothing for granted as he bids to close in on Roger Federer's grand-slam record.

Nadal is chasing a fourth US Open title which would move him to within one major win of matching Federer's tally of 20.

The field looks clear for Nadal as the only one of the 'big three' still standing at Flushing Meadows following the shock exits of Federer and defending champion Novak Djokovic.

But if Nadal needed a reminder that it will not be all plain sailing in New York, he got one when 20th seed Diego Schwartzman broke his serve four times in Wednesday night's quarter-final.

World number two Nadal came through 6-4 7-5 6-2 and faces Matteo Berrettini, the Italian 24th seed, for a place in the final against either Daniil Medvedev or Grigor Dimitrov.

Nadal has never played the 23-year-old, who reached his first grand slam semi-final after coming through five gruelling sets against Gael Monfils.

The Spaniard said: "He is having a great year. He's in the semi-finals, winning a lot of good matches. In the semi-finals of a grand-slam match you can't expect an easy opponent. You can't expect an easy match.

"I really believe that if you want to win tournaments, you need to go through tough opponents like I had against Marin (Cilic) and against Diego.

"He was playing great the whole event, and now another player is playing great. He's serving huge, big forehands, moving well, and big confidence because he's having a great year."

Berrettini was just nine when he first became aware of Nadal, watching his epic five-set final win over Guillermo Coria at the 2005 Italian Open.

"They were showing the match on the TV for free, but it was, like, a channel that was about cartoons," he recalled. "I was young. These guys, I mean, six hours. Come on! I want to catch my cartoons."

Dimitrov and Medvedev meet in the first semi-final, a match-up not many would have tipped in the side of the draw which featured Federer and Djokovic.

Injuries have seen Bulgarian Dimitrov, a former world number three, slip to 78 in the rankings making his win over Federer – his first in eight attempts – all the more surprising.

"It was that low that I don't even want to go there any more," he said of a miserable year.

"It was obviously injury, losing points, ranking. That's the lowest point of any player. The past six, seven months have been pretty rough for me. But I had somebody to lean on, my friends, my family.

"Next thing you know, you're almost end of the year, you have a result like that. It's pretty special to me."