The U.S. Open has waited 52 years for a man to have a chance at winning the Grand Slam, so what’s a few extra hours?

Top-ranked Novak Djokovic, undefeated in best-of-five matches this year as he pursues the Grand Slam, again lingered in long form play on Wednesday night in Arthur Ashe Stadium before rerouting to a romp of the sixth-seeded Matteo Berrettini, 5-7, 6-2, 6-2, 6-3.

Djokovic’s first set against Berrettini was the third straight time he had lost the opening frame, and also his most taxing set of the tournament. The first game lasted for 14 points; the sixth game needed 20 points. Though Djokovic was broken in the 11th game on a forehand passing shot winner by Berrettini and lost the set soon after, it was Berrettini who needed to leave the court to change out of his sweat-soaked attire just an hour and 17 minutes into the match.

Djokovic’s detours at this tournament have not led to despondency, but discovery.

The first set against Berrettini was the fourth set Djokovic has lost this tournament. As he did each time before, Djokovic took the information he gleaned and reprogrammed his game with increased precision. After hitting 17 unforced errors in the first set, he hit only three in the second and three in the third. Djokovic had five unforced errors in the fourth set.

Through force of will and persistence, he turned the match in his favor, and even won over some of the begrudging crowd. When he held for 5-2 in the third, after saving a Berrettini break point and extinguishing any hope for a comeback, Djokovic held his hand to his ear, imploring the crowd to recognize his indomitability as he moves closer to the Grand Slam, and a record 21st career major singles title.

After he got up a break early in the fourth set, Djokovic seemed to shift to a lower gear to coast to the finish, winning only two more points on return to conserve energy. When he wrapped up the victory after three hours and 27 minutes, Djokovic walked briskly to the net, wasting little energy on an elaborate celebration. He took several seconds to find the wristwatch he dons for the on-court interview to fulfill sponsor obligations.

“I was locked in, really, from the beginning of the second set,” Djokovic said in his on-court interview. “I took my tennis to a different level. This has been the best three sets I’ve played so far in the tournament, for sure.”

Djokovic has won the first 26 of the 28 matches he needs to complete the Grand Slam, but his 27th test may prove to be one of his toughest. On Friday night, Djokovic will face fourth-seeded Alexander Zverev, whose 16-match win streak includes a win over Djokovic in the semifinals of last month’s Tokyo Olympics.

Zverev needed only two hours and six minutes to complete his own quarterfinal victory hours earlier, avoiding delay by saving a set point in the tiebreak of his 7-6(6), 6-3, 6-4 win over Lloyd Harris.

Where Djokovic has been effective, Zverev has been efficient. Zverev has needed only nine hours and 23 minutes to complete his five wins here; Djokovic has needed 13 hours and 52 minutes.

In his news conference on Wednesday, Zverev showed confidence but recognized the task ahead of him.

“Against him you prepare that you have to play the best match that you can,” Zverev said of facing Djokovic. “You have to be perfect, otherwise you will not win.

“Most of the time you can’t be perfect,” Zverev added. “That’s why most of the time people lose to him.”