March 22 (UPI) -- Tennis star Serena Williams might be out of the Miami Open, but she says she's making progress.
Williams' run at the 2018 version of the tournament came crashing to a halt after just 77 minutes of play Wednesday against Naomi Osaka. The Indian Wells champion defeated Williams in straight sets, 6-3, 6-2 at the stadium court on Key Biscayne.
The eight-time Miami Open champion and 23-time Grand Slam victor did not do a post-match interview after her loss to the 20-year-old, but posted a message for her fans Thursday on Instagram.
"Four months ago I could not walk to my mailbox...but I will keep going forward and I'll get there," Williams wrote. "#StrongSure #WhatIsYourS."
The "#WhatIsYourS" hashtag is a reference to a campaign Williams started with a message on social media on March 7. She is wearing and giving out pins with the letter "S" and challenging her fans to come up with one "S" word in their lives that means something to them.
She says when she wears her "S" pin she represents strength and sureness.
Williams used the caption for a photo of herself competing in a Spartan race. She has participated in the obstacle course contests several times, along with husband Alexis Ohanian and sister Venus Williams.
Venus battles Russian Natalia Vikhlyantseva in a round of 64 match at 11 a.m. Friday at the Miami Open. She currently sits at No. 8 in the WTA Rankings, while Serena is ranked No. 491.