Aryna Sabalenka managed to overcome a contentious moment with the umpire to beat Elise Mertens at the Porsche Tennis Grand Prix.
Sabalenka and Mertens are former doubles partners, and have actually won two Grand Slam titles together.
Her victory over Mertens was actually the first match of the clay court season for Sabalenka, who received a walkover to the Stuttgart quarter-finals after Anastasia Potapova withdrew.
Despite beating her former doubles partner in straight sets, it was not completely plain-sailing for Sabalenka following a disagreement with the chair umpire.

Aryna Sabalenka reveals what the umpire told her after the match
With Sabalenka facing a break point at 3-3 in the first set, her shot was called out and Mertens took the advantage.
However, the Belarusian disagreed with this call and asked umpire Miriam Bley to check the mark.
Sabalenka then took matters into her own hands and grabbed her phone to take a picture of the mark, which resulted in Bley giving her a warning for unsportsmanlike conduct.
Despite going a break down at this point, Sabalenka was able to recompose and beat Mertens, 6-4 6-1.
When speaking in her on-court interview after the match, Sabalenka was asked about the incident and actually revealed that she felt Bley gave her a stronger handshake than an umpire ever has before.
“Yeah, I felt how the referees p***** probably by the picture I took,” said Sabalenka. “When I gave her handshake, that was a very interesting look and a very strong handshake, never had it before.”
Sabalenka was subsequently asked if she wanted to squeeze back on the handshake, but she quickly dismissed this, “No it’s okay, why would I play this game with someone like her, it’s okay.”
In a now deleted Instagram story, Sabalenka also showed the picture that she took of the ball mark that appeared to show it catching some of the line.
“Just for you guys (laughing face emoji),” the post read. “Apparently this is out (another laughing face emoji).”
Aryna Sabalenka explains how she overcame her frustration over the ball mark incident
Unsurprisingly this contentious issue was also brought to Sabalenka in her post-match press conference.
When questioned over whether she still believed the ball was in, Sabalenka adamant that the umpire should have changed her decision.
The three-time Grand Slam champion also explained how she managed to put this to one side and win nine of the next 10 games to take the match.
“Yeah, it was definitely in,” said Sabalenka. “I understand. I mean, everyone can make mistakes and I’m not the one who is going to be complaining with the referee. I’m usually quite respectful.
“But I think you cannot make these kind of mistakes. I think you have to, if you make the mistake, I think you have to have guts to admit it and make a call. I guess not everyone have the guts to do that, but it’s okay.
“Once again, everyone can make mistake, and as the time, not the time go, but with a little bit of time, I had time to cool down, let’s say like that, and I kind of like let it go, the situation. And it’s okay, whatever happens there.”

Sabalenka will now put this incident completely to bed, as she takes on Jasmine Paolini in the Stuttgart semi-finals.
This is the second successive tournament that they have played a semi-final match, with Sabalenka beating Paolini in Miami.
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