So far, Novak Djokovic’s performances at the U.S. Open are as boring as watching injuries heal.

Not Djokovic’s fault. But for a second consecutive time, the defending champ was not required to work through a match to continue his move through the tournament, now into the fourth round.

On Wednesday, Djokovic’s scheduled opponent, Jiri Veseley of the Czech Republic, defaulted shortly before he was to take the court because he hadn’t recovered from forearm inflammation suffered the previous week.

On Friday, Djokovic was leading Russia’s Mikhail Youzhny, 4-2, in the first set when the veteran Youzhny, who is 34, suffered a left hamstring strain and retired. They had played a mere 31 minutes.

So going into the tournament’s second week, Djokovic has “won” three matches while playing fewer than four sets.

Given that Djokovic — now 29 and with plenty of mileage on his tennis odometer — arrived at Flushing Meadows with a left wrist problem, then developed a sore right arm in his first-round victory over Poland’s Jerzy Janowicz, he was not complaining.

“This particular situation I never had in my Grand Slam career,” said Djokovic, who has won 12 major titles.

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Only Roger Federer, with 17, Pete Sampras and Rafael Nadal, 14 apiece, have won more.

“But, considering the stage of the season, you know, the amount of matches I’ve played” — 57 this year, of which he was won 52 — “what I’ve been through with my body, I think it’s actually good to have some days off and then shorter matches,” he said. “ . . . From the other side, sure, as you are approaching the second week of the Grand Slam, you want to have match play . . . But I’m not too concerned about my game and, health-wise, I feel much better than I did at the beginning of the tournament.”

He sympathized with the fans who “pay tickets to come to watch.” But since his was the last of three afternoon matches scheduled in Arthur Ashe Stadium, he was free to remain on court and practice for roughly an hour.