On paper, it was a seemingly uneventful, straight-sets victory for Pablo Carreno Busta, a 6-4, 6-4, 6-2 dismissal of Diego Schwartzman in a U.S. Open quarterfinal that lasted less than two hours.

But it all might have been different Wednesday if not for a pivotal sequence in the second set, when Schwartzman led 4-3 and 40-0, with an opportunity to turn it all around, perhaps for good.

Instead Carreno Busta, a Spaniard seeded 12th, stormed back to win that game, break the 29th-seeded Schwartzman in the next game, then put away the set and in effect the match.

“Of course, it was the most important moment of the match,” said Carreno Busta, who will next meet the winner of the late Sam Querrey-Kevin Anderson quarterfinal.

“It was the key, because when I was 4-3 and love-40, it was a really tough mentally moment. I just tried to focus on the next point, step by step, you know, point by point. Finally, I did it.”

Said Schwartzman, an Argentine: “I think sometimes that kind of game changes the match. I had three break points in that game, close break points.

“I think he played really well, two break points, and then I did one forehand mistake. Tough to understand. But then I think Pablo just played better than me.”

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Carreno Busta won six of his eight break points in the match; Schwartzman won two of 10.

Carreno Busta reached his first Grand Slam quarterfinal earlier this year at the French Open, on clay, which generally is considered his best surface. Now this.

It helps that he has had a favorable draw. Schwartzman was the first seeded player he faced.

“When you have this draw, you have to do your best to take advantage, so I think that is a really good tournament for me,” he said. “I know that I didn’t win matches against top players, top 10 or top 20 players, but I am very happy with my tournament.

“The draw, sometimes you are lucky, sometimes you are unlucky.”