Aryna Sabalenka took a photograph on court of a disputed ball mark during her quarter-final victory over Elise Mertens at the Stuttgart Open.
World number one Sabalenka disagreed with an "out" call on her shot when she was break point down against Mertens.
At the changeover, with Sabalenka trailing 4-3, the Belarusian asked umpire Miriam Bley to check the mark, before walking over to see it herself.
She then took a photograph, external of the mark with a member of her team's phone before receiving a warning for unsportsmanlike conduct from Bley.
Sabalenka did not let the incident distract her, regrouping to break back immediately and going on to win 6-4 6-1.
She shook hands with Bley at the end of the match but said in her on-court interview: "When I gave her a handshake, there was a very interesting look and a very strong handshake. Never had it before."
Asked if she squeezed the hand back, Sabalenka said: "No, it's OK. Why would I play this game with someone like her? It's OK."
Sabalenka will face Jasmine Paolini for a place in Monday's final after the Italian beat Coco Gauff 6-4 6-3.
Earlier, Jelena Ostapenko continued her dominance over Iga Swiatek, beating the world number two 6-3 3-6 6-2 to extend her unbeaten winning streak against the Pole to six matches.
Ostapenko is the first player to beat five-time major champion Swiatek on every surface - once on grass, four times on hard courts and now once on clay.
Swiatek often struggles against Ostapenko's powerful groundstrokes which rush her forehand and draw out the errors in her game.
The Pole came into the match with an 11-1 record in Stuttgart, having won the title in 2022 and 2023, but she could not fend off Ostapenko.
Ostapenko hit 29 winners to Swiatek's 17, with eight double faults not helping Swiatek as Ostapenko attacked her second serve.
Ostapenko broke Swiatek's serve three times to take the first set but was scrappier in the second, allowing Swiatek to level the match.
But Ostapenko won 12 of the first 15 point of the deciding set to take control, eventually taking the match on a long Swiatek forehand.
"She's a great clay-court player but I won the French [Open] as well, so I can say the same thing about myself, " the 27-year-old said.
"I have so much respect to her and her team but every time I step on the court with her, it's a battle and I'm ready for it."
Ostapenko will face a semi-final against Russia's Ekaterina Alexandrova, who beat third seed Jessica Pegula 6-0 6-4.