PARIS – The first obvious sign of trouble for Novak Djokovic came when he stepped onto Court Philippe Chatrier with a rather large square of beige athletic tape on the back of his neck.

The next indication came on the very first point of his French Open quarterfinal against Pablo Carreno Busta, when Djokovic let a ball toss drop and abandoned his serve mid-motion.

Soon enough, Djokovic was flexing and stretching his left arm or hitting it with his racket. Off to a slow start Wednesday night, Djokovic received massages from a trainer, righted himself and beat Carreno Busta 4-6, 6-2, 6-3, 6-4 to reach the semifinals at Roland Garros for the 10th time.

"I definitely didn't feel great coming into the court today. A few things happened in the warmup," the No. 1-ranked Djokovic said, without going into specifics.

"I had some neck issues and some shoulder issues. I'll just say that. I mean, I don't want to get really too much into it. Obviously I'm still in the tournament, so I don't want to reveal too much. I'm feeling OK.

"As the match progressed, I warmed up my body, and the pain kind of faded away. It allowed me to play better and better and feel better."

Djokovic will face No. 5 Stefanos Tsitsipas in Friday's semifinals. Tsitsipas reached his first French Open semifinal with a 7-5, 6-2, 6-3 victory over 13th-seeded Andrey Rublev.

Djokovic is righthanded, but the left side is important, too. He uses it for his two-fisted backhand and to throw the ball on serves. Whatever impediment there was to his play, whatever the pain level might have been, the issue was, at the very least, a distraction.

Carreno Busta, for his part, had at least a bit of doubt about what was going on.

"Maybe it's the pressure or something. ... I mean, he continues playing normal, no?" the 17th-seeded Spaniard said. "I don't know if he's [in] pain really. ... Ask him."

This was a rematch from the U.S. Open last month, when Djokovic was disqualified for inadvertently hitting a line judge in the throat with a ball he smacked in anger. That went into the books as a loss and remains the only blemish on Djokovic's 36-1 record in 2020.

"I'm over it," he said. "I'm not thinking about it at all. I mean, zero percent."

No. 2 Rafael Nadal faces No. 12 Diego Schwartzman in the other semifinal Friday. Nadal eyes a 13th championship at the French Open, which would give him 20 majors overall, equaling Roger Federer's record for men.

In the women's semifinals Thursday, it will be Sofia Kenin vs. Petra Kvitova, and Iga Swiatek vs. Nadia Podoroska.

Podoroska, ranked 131st, is the first female qualifier to get to the final four at the French Open. Kenin and Kvitova are the only women who have reached the fourth round or better at all three of the Grand Slams played in this pandemic-hit year that forced the cancellation of Wimbledon.