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At 38 years old, the former world No.1 became the oldest semi-finalist in ATP Masters 1000 history with this win in his first clash with the 26-year-old Belgian.

Djokovic, who battled through a leg issue and heat exhaustion during his fourth-round win against Jaume Munar, again struggled physically during the opening set against Bergs.

Yet he shook off what appeared to be a problem with his left foot to reach the last four at a Masters 1000 event for a record-extending 80th time.

Djokovic initially served for the match after breaking Bergs’ serve for 5-4 in the second set, but a spirited Bergs immediately drew level with a high-quality return game.

In the next game, Djokovic repelled four Bergs overheads and a swinging volley to prevail in one of the points of the tournament en route to breaking serve again, and this time the 100-time ATP Tour title winner made no mistake in closing out the win.

“I was just trying to stay alive to be honest on the court," Djokovic said.

"My first encounter with Bergs. He’s a great guy. Obviously, a lot of firepower in his game. At times I just tried to play an extra ball in the court and make him miss the ball, and that’s what happened. I should have closed out the match at 5-4. He played a good game, again I was a little bit too passive.

“Very challenging conditions these days for all the players, and I was just trying to stay alive on the court. I’m glad to overcome this hurdle.”

Djokovic is now two wins away from a record-extending 41st Masters 1000 crown, and his first since Paris.

Standing between him and a spot in the Shanghai championship match is qualifier Valentin Vacherot, who upset No.10 seed Holger Rune 2-6 7-6 (7-4) 6-4 in their quarter-final.