Japanese superstar Naomi Osaka was on Sunday threatened with disqualification from the French Open if she persists with her controversial media boycott, officials said.
"We have advised Naomi Osaka that should she continue to ignore her media obligations, she would be exposing herself to possible further code of conduct infringement consequences," said a statement from the four Grand Slam tournaments after the world number two was fined $15,000.
"Repeat violations attract tougher sanctions including default from the tournament and the trigger of a major offence investigation that could lead to more substantial fines and future Grand Slam suspensions."
Osaka, a four-time Grand Slam title winner and sport's highest-earning female athlete, was sanctioned for refusing to hold a press conference after her opening 6-4, 7-6 (7/4) victory over Romanian world number 63 Patricia Maria Tig.
The 23-year-old had said on the eve of the tournament that she would not carry out any media obligations, claiming news conferences are detrimental to her mental health.
She likened traditional post-match inquests to "kicking people when they're down".
French Tennis Federation president Gilles Moretton had described Osaka's vow of silence as "a phenomenal error".
The four Grand Slam events - Wimbledon, the French, Australian and US Opens - said they had written to Osaka "to check on her well-being and offer support".
"She was also reminded of her obligations, the consequences of not meeting them and that rules should equally apply to all players.
"Naomi Osaka today chose not to honour her contractual media obligations. The Roland Garros referee has therefore issued her a $15,000 fine."
Later on Sunday Osaka's position became more entrenched when she tweeted in response to her fine: "Anger is a lack of understanding. Change makes people uncomfortable."
After her match, Osaka agreed only to a cursory on-court TV interview.
"For me, playing on clay is a work in progress," said the reigning US and Australian Open champion on a sun-kissed Court Philippe Chatrier.
"Hopefully the more I play, the better I will become."
And that was that from a player who has now strung together 15 successive Grand Slam match wins.
'It's not good'
The Grand Slam Board said Osaka's refusal to take part in media duties put opponents at a disadvantage.
"There is nothing more important than ensuring no player has an unfair advantage over another, which unfortunately is the case in this situation if one player refuses to dedicate time to participate in media commitments while the others all honour their commitments."
If Osaka was to be disqualified, it would be as sensational as Novak Djokovic's default at last year's US Open where the world number one was booted out for hitting a line judge with a ball.
"I was always trying to follow the rules and be fair not only on the court but off the court as well. Now it's up to them to decide what's going to be," said former two-time Wimbledon winner Petra Kvitova after her opening win.
Osaka's compatriot Kei Nishikori added: "It's not good but I understand her situation. So it's good and bad."
Osaka's defiant stand overshadowed the opening day of the 2021 French Open which saw two-time runner-up Dominic Thiem crash at the first hurdle.
Fourth seed and US Open champion Thiem, who had never been beaten in the first round in seven previous visits, squandered a two-set lead to lose 4-6, 5-7, 6-3, 6-4, 6-4 to 35-year-old Pablo Andujar of Spain.
"Losing after being two sets to zero up, it's very strange to me, and I have to think about what's wrong at the moment," said Thiem.
Andujar said his recent win over Roger Federer in Geneva ranked higher.
"For me, he is like a myth."
Fresh from her first career clay court title in Madrid, Belarusian third seed Aryna Sabalenka eased past Croatian qualifier Ana Konjuh 6-4, 6-3.
World number five Stefanos Tsitsipas rounded off the day with a 7-6 (8/6), 6-3, 6-1 over Jeremy Chardy.
The Greek is widely tipped as a potential champion should 13-time winner Rafael Nadal or world number one Novak Djokovic falter.
However, there was nobody inside the cavernous Chatrier Court to assess his credentials as the match started just before a 9pm Covid-19 curfew came into effect.
Germany's Alexander Zverev, seeded sixth, battled back from two sets down to beat compatriot Oscar Otte 3-6, 3-6, 6-2, 6-2, 6-0.
It was Zverev's seventh win from as many five-set matches at Roland Garros.
German 26th seed Angelique Kerber, a three-time major winner, was the day's biggest loser in the women's draw, going down to 6-2, 6-4 Ukrainian qualifier Anhelina Kalinina.
French Open results on Sunday, the first day of the 2021 tournament at Roland Garros (x denotes seeding):
Alexander Zverev (GER x6) bt Oscar Otte (GER) 3-6, 3-6, 6-2, 6-2, 6-0
Roman Safiullin (RUS) bt Carlos Taberner (ESP) 7-6 (7/4), 1-6, 6-0, 6-2
Laslo Djere (SRB) bt Corentin Moutet (FRA) 6-3, 6-7 (10/12), 7-6 (7/2), 7-5
Miomir Kecmanovic (SRB) bt Dan Evans (GBR x25) 1-6, 6-3, 6-3, 6-4
Karen Khachanov (RUS x23) bt Jiri Vesely (CZE) 6-1, 6-2, 6-3
Kei Nishikori (JPN) bt Alessandro Giannessi (ITA) 6-4, 6-7 (4/7), 6-3, 4-6, 6-4
Henri Laaksonen (SUI) bt Yannick Hanfmann (GER) 6-1, 6-3, 4-6, 6-2
Roberto Bautista Agut (ESP x11) bt Mario Vilella Martinez (ESP) 6-4, 6-4, 6-2
Alejandro Davidovich Fokina (ESP) bt Mikhail Kukushkin (KAZ) 6-4, 6-4, 6-3
Botic van de Zandschulp (NED) bt Hubert Hurkacz (POL x19) 6-7 (5/7), 6-7 (4/7), 6-2, 6-2, 6-4
Fabio Fognini (ITA x27) bt Gregoire Barrere (FRA) 6-4, 6-1, 6-4
Marton Fucsovics (HUN) bt Gilles Simon (FRA) 6-4, 6-1, 7-6 (7/5)
Pablo Andujar (ESP) bt Dominic Thiem (AUT x4) 4-6, 5-7, 6-3, 6-4, 6-4
Stefanos Tsitsipas (GRE x5) bt Jeremy Chardy (FRA) 7-6 (8/6), 6-3, 6-1
Enzo Couacaud (FRA) bt Egor Gerasimov (BLR) 7-6 (7/3), 6-4, 6-3
Pablo Carreno Busta (ESP x12) bt Norbert Gombos (SVK) 6-3, 6-4, 6-3
Marcos Giron (USA) bt Grigor Dimitrov (BUL x16) 2-6, 4-6, 7-5, 3-0 - retired
Guido Pella (ARG) bt Daniel Elahi Galan (COL) 6-3, 7-6 (7/4), 7-5
Mackenzie McDonald (USA) bt Emil Ruusuvuori (FIN) 4-6, 6-3, 7-6 (7/4), 6-3
Christian Garin (CHI x22) bt Juan Ignacio Londero (ARG) 3-6, 6-4, 7-6 (8/6), 6-2
Danielle Collins (USA) bt Wang Xiyu (CHN) 6-2, 4-6, 6-4
Anhelina Kalinina (UKR) bt Angelique Kerber (GER x26) 6-2, 6-4
Elena Rybakina (KAZ x21) bt Elsa Jacquemot (FRA) 6-4, 6-1
Nao Hibino (JPN) bt Nina Stojanovic (SRB) 7-6 (7/4), 6-2
Elena Vesnina (RUS) bt Olga Govortsova (BLR) 6-1, 6-0
Petra Kvitova (CZE x11) bt Greet Minnen (BEL) 6-7 (3/7), 7-6 (7/5), 6-1
Victoria Azarenka (BLR x15) bt Svetlana Kuznetsova (RUS) 6-4, 2-6, 6-3
Clara Tauson (DEN) bt Ekaterine Gorgodze (GEO) 6-4, 6-2
Leylah Fernandez (CAN) bt Anastasia Potapova (RUS) 6-2, 6-1
Madison Keys (USA x23) bt Oceane Dodin (FRA) 6-3, 3-6, 6-1
Anastasia Pavlyuchenkova (RUS x31) bt Christina McHale (USA) 6-4, 6-0
Ajla Tomljanovic (AUS) bt Kateryna Kozlova (UKR) 6-2, 6-4
Aliaksandra Sasnovich (BLR) bt Diane Parry (FRA) 6-3, 3-6, 6-3
Aryna Sabalenka (BLR x3) bt Ana Konjuh (CRO) 6-4, 6-3
Katerina Siniakova (CZE) bt Marie Bouzkova (CZE) 6-0, 4-6, 6-2
Veronika Kudermetova (RUS x29) bt Amanda Anisimova (USA) 7-6 (7/5), 6-1
Paula Badosa (ESP x33) bt Lauren Davis (USA) 6-2, 7-6 (7/3)
Danka Kovinic (MNE) bt Clara Burel (FRA) 6-3, 7-6 (10/8)
Ana Bogdan (ROM) bt Elisabetta Cocciaretto (ITA) 6-1, 6-3
Naomi Osaka (JPN x2) bt Patricia Maria Tig (ROM) 6-4, 7-6 (7/4)