Juan Martin del Potro admits he considered giving up tennis altogether.

While undergoing three wrist surgeries that kept him off the tour for extended periods and threatened to derail his career for good, del Potro contemplated the worst.

"Well, I was really close to quit tennis because after the first surgery, the second one, and in the end the third one, it was really, really sad moments for me," the 6-foot-6, 27-year-old Argentine said. "Nobody knows what should I have to fix my problem."

Buoyed by the support of family and friends, del Potro persevered and now he's aiming to win his second US Open title since 2009, when he beat Rafael Nadal and Roger Federer back-to-back en route to the Open crown. This time he'll have to do it as a wildcard entry into the Open.

After taking out No. 11 David Ferrer in straight sets on Saturday, del Potro will attempt to continue his comeback run against No. 10 Dominic Thiem in a fourth-round match beginning Monday morning in Arthur Ashe Stadium .

"I think what he's done has been amazing," said No. 2 Andy Murray, who meets No. 22 Grigor Dimitrov in the night session and could face del Potro in the semifinals. "I'm not surprised at how well he's hitting the ball. He's always been a great ball-striker. I don't expect him necessarily to lose that. It's more the mentality that he's shown really has been the most impressive part.

"You know, [I'm] happy for him that he's managed to get himself back competing in the big events at the top again."

del Potro has had to alter his backhand due to the wrist injury, and now hits with more slice on that side as opposed to the flat two-handers he used to win the Open in 2009. Yet when he's crushing his massive serve and big forehand the way he's capable of, del Potro can beat anyone.

After the 2009 US Open -- when he ended Federer's run of five straight Open titles -- many observers thought the Argentine was on course to win multiple majors.

But because of his wrist issues, he has been off the tour for long stretches during the last six years. During that time, the Big Four of Federer, Nadal, Murray and Novak Djokovic have continued to rack up Grand Slam singles crowns.

"I can imagine how demoralizing that must have been, how tough it would have been to keep wanting to do it, keep fighting to do it," Murray said.

"Also your body, as well. Like when you don't play matches, hardly any matches for a long period, it takes time for your body to get used to it again."

del Potro returned to the tour in February after his third wrist surgery and has made the most of 2016.

Just last month, he took out both Djokovic, the world No. 1 and No. 5 Nadal en route to the gold-medal match in his native Argentina.

He ended up losing to Murray, who became the only man to win a second gold medal in singles.

"I think was different because the people in Argentina, in my hometown, they know what has been through to get there after my surgeries," he said. "It was a special moments for me. They really appreciate what I did to come back on tennis. They are proud to see me playing tennis again. I'm very proud to represent my hometown, my country. It was amazing for me at Rio."

While Murray is a favorite to get to the final on the bottom half of the draw, don't count out the huge-hitting del Potro, who knows how to win in Queens.

"It's tough to describe this moment for me," he said. "I'm so excited to play and show my tennis. After my third surgery, I was really close to giving up. And now I'm playing tennis again. This court, this crowd, this stadium, it means so much to me."

Follow Adam Zagoria on Twitter @AdamZagoria for updates throughout the U.S. Open.