Diego Schwartzman defeated reigning Nitto ATP Finals champion Alexander Zverev on Monday to reach the US Open quarter-finals for the second time in three years. The No. 20 seed, who triumphed in Los Cabos last month, will try to earn his first FedEx ATP Head2Head victory against second seed Rafael Nadal on Wednesday.

If the Argentine wins, he will reach the semi-finals of a Grand Slam for the first time.

"[I have to] hit very hard to the lines. No, I need to be focussed. Tomorrow is going to be a big day," Schwartzman said. "I need to study my games against him. I have many good games, very good matches against him. I had my chances against him in many matches, but I wasn't able to win those opportunities against him. You never know when the next opportunities are going to come. Maybe it's the next match against him. I need to be ready."

Before the match, ATPTour.com caught up with Schwartzman's coach, Juan Ignacio Chela.

Coming into this match, I’m sure Diego was very confident. How happy are you with how things went today, especially after the first set was back and forth?
Diego started the match fully confident. He won each of his first three matches in straight sets, so he came into the contest mentally and physically fresh. We knew going into this match, against one of the best players in the world, that things would get complicated. Sascha made more errors than usual and his serve wasn’t as strong as it normally is.

Diego took advantage of the opportunities presented to him. He stayed positive and didn’t lose his composure, even after losing that first set. He played a solid, aggressive style the rest of the match and kept lifting his game.

Diego was talking about how Sascha didn’t serve his best, but also that he [Diego] is also a very good returner. How much do you think the pressure of Diego’s return helped cause all of the double faults [17] and some of that during the match?
Diego is one of the best returners in the world. He always applies pressure on his opponents’ serves. But it also looked to me like Zverev wasn’t feeling confident about his serve and he committed more double faults than usual. He was just more vulnerable.

It’s not the first time Diego has made it this far here. He had a big tournament here a couple of years ago. What’s different about Diego this year versus two years ago?
More than anything, he’s gained valuable experience. He’s been in these types of situations before. Now, he’s got the confidence and experience to fall back on. He’s also physically a lot stronger than he was before. I’m not sure who his next opponent will be [Nadal], but whoever it is, Diego will be ready.

Diego has been playing well this summer, and winning in Los Cabos was a big moment for him. His losses have been against guys playing good tennis. Have you seen his confidence growing over the past couple of months?
Yes. Even before [the North American hard-court season], Diego was playing well. Near the end of the clay-court season he had a strong result in Rome [semi-finals] and he had a good showing at Wimbledon [l. to Berrettini in five sets, R3]. After a short rest, he worked hard to prepare for tournaments on hard courts in Canada and around North America.

Winning a title [at Los Cabos] boosted his belief in himself and paved the way for the rest of the summer. This is exactly what we wanted: an impressive run at the US Open, the most important tournament of the summer.

His Wimbledon loss was very tight. How much do you think that motivated him to keep building forward?
Wimbledon was a weird tournament; not bad, though. He won his first two matches and had match points in the third [against Berrettini]. He was that close to moving into the second week at Wimbledon.

It was a tough, complicated match and it was too bad he couldn’t close things out with the match point opportunities he had, but that was another learning experience for Diego and a chance for us to build from that.

I don’t know if you know this but he thought he was playing Berrettini next. How funny was that, that he wasn’t really sure because he thought they were playing at the same time?
Yeah [laughs]. While Diego was playing in [Arthur] Ashe [Stadium], they were showing updates of Berrettini’s match and of him celebrating after the win. So Diego figured that’s who was next. Diego doesn’t like to look at the draw, he prefers to take it one match at a time, so he doesn’t know what his bracket looks like.

He was surprised when he learned he’d be playing the winner of Cilic and Nadal. Either way, he’s going to have to play his best tennis against a fine opponent.

If he does play Rafa, he’s had more success against Cilic than Rafa. How important is it to go into the match, mentally still believing he can still win, even if hasn’t had as much success?
Diego’s playing at a very high level and I like his chances regardless of the opponent. If Cilic comes through, perhaps that’s good for us because we match up well against him and have beaten him in the past. We’ve had our chances against Rafa in the past, too, if not the wins.

If there’s one thing he could do when he goes out on the court, what would you want to see from Diego and why?
I want to see that fighting spirit. I want to see him being aggressive, moving into the court and using his legs, tracking down every shot and transitioning from defence to offence. Those are our keys to victory.