After Sabalenka secured the 6-3 6-2 win, Kostyuk walked straight over to the umpire to shake her hand and then back to her seat, refusing to meet Sabalenka at the net for the customary handshake.
There were then boos from the crowd at Roland Garros and again as Kostyuk made her way off the court.
Kostyuk was booed as she left the court. - Clive Brunskill/Getty Images
Sabalenka fielded some difficult questions in her post-match press conference, including from one reporter who accused her of “twisting it as if Ukrainians hate you” and “avoiding” questions asking her to condemn the war, with Belarus being used as a key staging ground for Russia’s war in Ukraine.
Sabalenka said in March that she struggled to understand the “hate” she encountered in the locker room amid strained relations between some players following Russia’s invasion of Ukraine.
“First of all, when I get questions about Ukrainians, they [journalists] ask me: ‘So, you know that they hate you?’ So I’m answering the questions like: ‘If they hate me.’
“About the war situation, I said it many, many times, nobody in this world – Russian athletes, Belarusian athletes – supports the war. Nobody. How can we support the war? Normal people will never support it.
“Why do we have to go loud [public] and say things, that’s like saying ‘one plus one is two,’ you know, of course we don’t support war. And if you could affect the war in any way, if we could stop it, we would do it, but unfortunately it’s not in our hands.”
Sabalenka advanced to the second round in straight sets. - Christophe Ena/AP
Sabalenka later added that she understands why Ukrainian players don’t shake her hand and said Kostyuk didn’t deserve to be booed by the crowd.
Russian and Belarusian players are currently still competing on the tours as neutral athletes without their flag or country displayed.
After winning the ATX Open in Texas in March, Kostyuk also refused to shake hands with beaten Russian opponent Varvara Gracheva.
For more CNN news and newsletters create an account at CNN.com