Months after dazzling with a jellyfish-inspired outfit at the Australian Open, Osaka walked onto Court Suzanne Lenglen in a sequined waistcoat blouse and a black mesh floor-length train before unveiling a layered yellow-brown and gold match dress.
"Honestly, it's very couture," Osaka said in her on-court interview about her kit.
"Funnily enough, I feel like... You know the Eiffel Tower at night when it's sparkly? I think I look like that a bit."
Siegemund, far more understated in attire, held her own once the contest began, but four-time Grand Slam champion Osaka quickly took control of the opening set and closed it out with minimum fuss.
As the blazing afternoon sun made conditions more difficult for players, Osaka allowed the momentum to shift in the next set, but the 16th seed saved a set point and powered back from 5-3 down to force a tiebreak and prevail.
"I felt really nervous, but for me, I haven't played on this court in a little while, so it's nice to get out here and play in front of everyone," Osaka added.
"It's really hot, so I hope everyone is drinking water."
Osaka takes on 2024 Paris Olympics silver medallist Donna Vekic in the next round after the Croat eased past local hope Alice Tubello.