NEW YORK -- Rafael Nadal's knee was bothering him. His decade-younger, barrel-chested US Open foe was bashing the ball.
Nadal, the defending champion, was two points away from falling into a two-set hole. Then he was two points away from dropping the third set. And then he was one point from losing the fourth set and being pushed to a fifth.
As all of those key moments presented themselves, he managed to come through. The No. 1-ranked Nadal overcame a shaky start Friday and used his customary relentless style to physically and mentally wear down No. 27 seed Karen Khachanov, eventually getting to the fourth round with an entertaining and back-and-forth 5-7, 7-5, 7-6 (7), 7-6 (3) victory.
The match lasted 4 hours, 23 minutes.
"I escaped a very tough situation,'' Nadal said, "so it's a great thing.''
The man he beat in last year's final at Flushing Meadows, No. 5 Kevin Anderson, got through his own tough test against an up-and-coming opponent, edging No. 28 Denis Shapovalov 3-6, 6-4, 6-4, 4-6, 6-4.
After Nadal ceded the opening set, he had a trainer put tape under his right knee, which has caused him problems off and on over the years. Nadal later got more wrapping there during a 10-minute break at 5-all in the second set while the retractable roof at Arthur Ashe Stadium was shut because of light rain.
Just before the delay, Khachanov had served for that set at 5-4, and three times was two points away from taking it. But he couldn't get closer than that. Nadal broke for 5-all and, after the delay, broke again to even it at a set apiece, aided by two double-faults from Khachanov. When Nadal earned that set with a passing shot that drew an errant volley, he crouched and yelled. Folks sitting in his guest box rose. A chunk of the crowd gave a standing ovation. Khachanov swatted a ball in disgust.
Nadal said the brief break was just what he needed.
"I just trying to calm myself for a moment. He was playing well,'' Nadal said. "But for me, the most important thing is have the right tempo when I am playing. For some moments I felt things were going too fast in my mind. I didn't take the time to do the right steps, to go to the ball with the right decision, with the right determination, with the right timing.''
The end of the third set was similar: Khachanov twice was two points from owning it and couldn't get across the line, helping Nadal with three double-faults in the tiebreaker. And while Nadal kept letting set points slip away, four in all, he made No. 5 count. It was a quintessential Nadal point: a 39-stroke exchange after the serve that featured so much defense from Nadal until Khachanov netted a backhand, then tossed his racket on the sideline.
"I needed that set, of course,'' Nadal said.
He had one more pivotal part to get through: Khachanov's set point in the fourth while ahead 6-5 as Nadal served at 30-40. But Khachanov put a forehand in the net there, and after a thrilling point that featured a drop shot, a lob, a leaping tweener by Khachanov and a volley winner by Nadal, they headed to another tiebreaker.
Nadal moves into the fourth round at Flushing Meadows for the 10th time in his past 11 appearances.
Also through to the fourth round is 2009 champion Juan Martin del Potro, who beat No. 31 seed Fernando Verdasco 7-5, 7-6 (6), 6-3.
Next up for del Potro, the No. 3 seed, is No. 20 seed Borna Coric.
Earlier Friday, 2016 champion Stan Wawrinka's return to the US Open ended.
Wawrinka was eliminated by No. 25 seed Milos Raonic of Canada 7-6 (6), 6-4, 6-3 in the third round, ending his nine-match winning streak in Flushing Meadows.
Wawrinka had to miss the tournament in 2017 and had two left knee surgeries. The three-time Grand Slam tournament champion from Switzerland was given a wild card into this year's tournament after his ranking fell too low with all his missed time, and he knocked out No. 8 seed Grigor Dimitrov in his opening match.
Raonic will face No. 11 seed John Isner in the fourth round.
In other men's third-round action, No. 9 seed Dominic Thiem won another lengthy match to reach the round of 16.
Thiem beat American Taylor Fritz 3-6, 6-3, 7-6 (5), 6-4 in a match that lasted 3 hours, 19 minutes.
Each of the last two sets took more than an hour before Thiem moved on to a matchup with Anderson.
In the previous round, Thiem won a five-set match that lasted 3 hours, 34 minutes against another American, Steve Johnson.
The Associated Press contributed to this report.