Serena Williams and Naomi Osaka
Serena Williams lost her opening round match at the Miami Open to Naomi Osaka. Pictured: Serena Williams meets Naomi Osaka of Japan after losing to her in straight sets during Day 3 of the Miami Open in Key Biscayne, Florida, March 21, 2018. Al Bello/Getty Images

Serena Williams could be facing a fine after failing to show up for her post-match press conference at the Miami Open on Wednesday.

Williams was taking part in just her second competitive tournament since returning from a 14-month absence from the sport due to pregnancy as she took on newly-crowned Indian Wells champion Naomi Osaka.

However, the American suffered a rare opening round exit as it was the 20-year-old who emerged victorious as she defeated her idol in a straight-set 6-3, 6-2 victory. This was Williams' second loss in a week following her third round exit against her sister Venus in California last week.

The former women's world No. 1 congratulated Osaka at the end of the match but was in no mood to face the media afterward as she failed to show up for the mandatory press conference.

According to the Express, Williams is now facing a $1,000 fine for not adhering to the tournament guidelines. She did, however, release a statement through the Women’s Tennis Association (WTA) soon after, touching upon the experience and how she aims to keep progressing.

"Every tournament is an opportunity for me to better understand the areas I need to improve to be my best," Williams wrote. "Naomi played a great match and I learn something each time I play. I look forward to continuing my return by progressing every day. I'm so grateful for my fans who continue to support me every step of this incredible journey."

Before the tournament, Williams claimed she would be taking her comeback step by step and will eventually return to her best as she battles off the rust from not playing tennis for over a year.

Meanwhile, Osaka was over the moon with her win, which comes just a couple of days after winning her first-ever career title at Indian Wells. She said she wanted to make sure Williams knew who she was after the match, citing the 36-year-old as the main reason she decided to play tennis.

"It's weird if you grow up watching someone and wanting to be exactly like them and then you have the chance to play them," Osaka said after the match. "It's sort of this respect thing, but you also want to win really bad. I don't really know how to describe it. I just wanted her to, in the end, like after the match, just know who I am and stuff."

Williams definitely does now as Osaka was also happy to hear her opponent shout at herself for motivation.

"Sometimes she plays matches where she doesn’t say ‘Come on!’ at all," Osaka explained. "That’s a little bit sad, because it’s like, ‘Do you think she’s trying?’ So I just wanted her say ‘Come on!’ once. I knew then maybe she would be trying a little bit. Sometimes when I’m in a really hard position when I’m serving, I’m like, ‘What would Serena do?'"

The Japanese-Haitian will now face Ukraine's Elina Svitolina in the round of 64 on Friday.