Arthur Rinderknech scrawled an unusual message on the camera after winning a Paris Masters match for the first time.
The Frenchman dropped the opening set to Tomas Machac and was serving to force a decider when his opponent retired injured.
Rinderknech apologised to his opponent before joking that it was "Halloween time" after advancing to the second round.
Machac's Paris Masters run ended in disappointment. After taking a close first set against Rinderknech, the world No. 25 started to struggle and went down an early break in the second, calling a physio.
After receiving a medical time-out, he looked to be recovering and drew level at 3-3. But Rinderknech broke again and was 15-0 up while serving for the set at 5-3 when Machac forfeited the match.
The Czech star waited at the net to shake hands with his opponent, looking defeated. "I'm sorry. Was it your achilles again?" Rinderknech asked before Machac confirmed his injury.
Commentator Mikey Perera said: "Well he had the medical time out earlier in the set. We thought maybe he recovered, he looked okay, he was winning games again. But just like that he said, 'No, I cannot continue.'"
After winning a match at one of his home tournaments for the first time, Rinderknech had the honour of signing the camera lens in celebration.
And he appeared to troll his opponent with a jokey message about Halloween. "Sorry Tomas, Halloween time. #TD," the Frenchman wrote.
The world No. 60 will now face either Alex Michelsen or 12th seed Hubert Hurkacz in the second round. Rinderknech has only been to the third round of a Masters 1000 tournament once at this year's Canadian Open and he'll be keen to repeat his run in Paris.
Twelve months ago, Rinderknech lost his opening match in the qualifying rounds at the Paris Masters. He'd also never won in his two main draw appearances.
Meanwhile, Machac will be hoping to recover in time for next week's ATP 250 event in Belgrade, where he would be the No. 6 seed in the draw.
The Olympic gold medallist in mixed doubles has been bogged down by several injury issues this year. He also retired injured at the Almaty Open less than two weeks ago and, during the Davis Cup group stage in September, had to quit in the middle of both of his singles matches.
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