The evergreen former world No.1celebrated turning 38 by earning revenge over Matteo Arnaldi in the quarter-finals of the ATP tournament on Thursday.
But Australian hope Alexei Popyrin missed the chance to enjoy a semi-final clash with the 24-time grand slam champ when he got knocked out by Britain's Cameron Norrie.
It appears after a poor claycourt season and with the start of the French Open just three days away, Djokovic may be running into form at the right time by the way he dismantled world No.39 Arnaldi, who had beaten the great Serb at the Madrid Masters last month.
Still not completely happy with his form, though, Djokovic, currently down at No.6 in the rankings, had a fit of temper in the second set, smashing his racquet into the clay behind the baseline after his serve had been broken to trail 3-1.
Then at 4-1 down, there was an alarming moment when he seemed to have jolted his right knee when stretching for a shot, but he recovered admirably to reel off the next five games for a 6-4 6-4 win.
Afterwards, the birthday boy apologised for his tantrum on a chilly evening in Switzerland.
"I'm sorry for the racquet, it's not a good example particularly for the young ones," Djokovic told the crowd in French in an on-court interview.
"Thanks for your support. I know that with the cold temperatures it's not easy to stay here."
Later he reflected: "I think I'm playing really good tennis. A straight-sets win, but it was much closer than the score indicates.
"I found the optimal state and balance, mentally and emotionally, to be able to play my best tennis when it was most needed. Hopefully I can carry that into tomorrow."
Popyrin, who believes he's finding some of his best form after a poor start to the year beset by injuries, illness and a coaching break-up, couldn't find the form later to land that semi-final crack at Djokovic, whom he beat at last year's US Open.
He will rue a missed opportunity in the first set when he served for the stanza at 5-4, only to get broken and lost a tight tiebreaker, but the chilly, rainy conditions didn't suit him as he succumbed 7-6 (8-6) 6-4.
American top seed Taylor Fritz lost to sixth seed Hubert Hurkacz 6-3 7-6 (7-5), while fourth seed Karen Khachanov lost 4-6 6-4 6-4 to 128th-ranked Austrian qualifier Sebastian Ofner.
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