SHANGHAI, China (AFP) — Novak Djokovic proved his staying power on Friday, beating an opponent 18 years his junior 6-7 (4/7), 6-1, 6-4 to claim the last spot in the Shanghai Masters semifinals.

The 37-year-old’s victory over the Czech Republic’s Jakub Mensik came a day after one of his greatest rivals and contemporaries, Rafael Nadal, announced he would retire in November.

The Serbian, who is aiming for a 100th singles title in Shanghai, will next face world No. 7 Taylor Fritz after the American beat Belgium’s David Goffin 6-3, 6-4 earlier on Friday.

“Overall, big battle, it took the best out of me to win it,” Djokovic said after the match.

Both Djokovic and 65th-ranked Mensik brought serious firepower to the court, their hard-hitting rallies driving the stadium wild with tension.

The first set was closely fought, with Djokovic’s break in the ninth game matched immediately by Mensik in the next.

The veteran pulled ahead early in the tiebreak, but seemed to lose focus, allowing the 19-year-old to come from behind to win.

The 24-time Grand Slam champion dominated the second set though, breaking in the second and sixth game.

Mensik recovered to pile on the pressure again in the third, but Djokovic got a crucial break in the fifth game to be crowned winner.

Djokovic called his opponent “one of the best players we have on the tour,” adding “the future is very bright for him.”

“These kind of matches against teenagers is something that really motivates me... and pushes me to really dig deep and to show to the world that I still got it, you know, and my legs can still go the distance with the young guy,” he said.

Djokovic’s triumph came the day after the retirement announcement from Nadal — who he called “the greatest rival that I ever had” — was not lost on him.