John Isner's coach Justin Gimelstob has claimed that the big-serving American is starting to address his weaknesses in a bid to improve his results.
The 30-year-old has picked up 10 career titles, but has only been beyond the fourth round of a Grand Slam once, when he reached the US Open quarter-finals in 2011.
However, Gimelstob is confident that Isner's work on making his game well-rounded could make him more successful.
He told the US Open official website: "It's working. His weaknesses have improved. He's returning serve better. His backhand has improved. He's improved moving forward at the net.
"I'm proud of his progress. I'm proud he's committed to make changes and to do the work that he needed to do to improve, even at the later stages of his career.
"He's 6'10''. For him to get through these matches, breaking serve more often, ending matches quicker, and having more of an energy reserve when he does play the top players, it's a huge part of giving him an opportunity to be more successful."
Isner faces Roger Federer on Monday for a place in the last eight.
