Novak Djokovic said he was overwhelmed by the news that he would be the only active member of the so-called Big Four.

With Roger Federer and Andy Murray already leaving the sport, Rafael Nadal announced on Thursday that he would also be hanging up his racket at the end of the season. Djokovic has spent nearly two decades battling his biggest rivals and has recorded the most Grand Slams of all, 24, compared to Nadal’s 22, Federer’s 18 and Murray’s three. The Brit, of course, lost eight Grand Slam finals, all against Djokovic or Federer.

“We knew this moment would come sooner than later, but it’s still a shock,” Djokovic said after defeating Jakub Mensik and reaching the semifinals of the Shanghai Masters. “Also for Roger a few years ago when he announced his retirement and also for Andy this year. It’s a bit overwhelming for me. I don’t know what to make of it. I still enjoy competing, but a part of me has stayed with them, a big part of me.”

There appears to be no prospect of Djokovic following his former rivals any time soon, and the 24-time Grand Slam champion withstood the challenge of Czech teenager Mensik – almost 20 years his junior – to triumph 6-7 ( 4), 6:1, 6 -4.

Djokovic seemed to have the first set under control, but then he spiraled completely out of control, losing his break advantage and then the tiebreak. However, he formed well at the start of the second period, and the only real moment of concern came midway through the third when he appeared to feel pain in his left knee.

Djokovic, who still wears a brace on his right knee after surgery after the French Open, said: “To be honest, it’s a strange feeling, those few points in that match, but after that everything was fine.”

“So hopefully when it cools down I won’t have any problems with that because I already have problems with my right knee so it wouldn’t be great.”

Djokovic knows the 19-year-old Mensik well, having trained with him, but was determined to get another win for the old guard. “These types of games against teenagers are something that really motivates me, keeps me going and pushes me to really dig deep and show the world that I still have it in me and I still have it Distance can go young people,” he said. “That’s why I’m super happy that I managed to win this very challenging game.”

In the final four games, Djokovic will face seventh seed Taylor Fritz, who ended David Goffin’s streak with a 6-3, 6-4 win.