The French Open was only the third tournament appearance for Williams, 36, since claiming the 2017 Australian Open title, as she had been on maternity leave for the birth of her daughter in September. It was an emphatic performance for Muguruza, who made it to the fourth round of the US Open last year and just the second round of the Australian Open earlier this year.
"I think the slower the surface is, the better for her", Wozniacki said.
But the show rolls on at Roland Garros for Sharapova, Muguruza and fellow title hopefuls Halep and Kerber, who couldn't have been more impressive on Monday.
Serena had gone into that match wearing her striking all-black catsuit but she admitted she had had to tape her serving arm to try and protect the injury.
Williams' voice quivered as she said she can't serve because of a problem with her right pectoral muscle. "Right now, I can't actually serve so it's actually hard to play when I can't physically serve".
"It was a great match, and the way I played gives me confidence that I did everything well", said the Romanian world No.1. "I mean, I think she made everyone wait a little bit".
On a brighter note, Williams played in a doubles match-up with her sister Venus.
Despite her first loss to Muguruza in their fourth meeting, committing 27 unforced errors and getting broken six times, Sharapova said she saw signs of hope in her form as she builds towards Wimbledon next month. The Russian, a marmite figure on the WTA Tour, next meets the 2016 Roland Garros victor, Garbine Muguruza - Sharapova leads their head-to-head meetings 3-0. She beat Kristyna Pliskova in a two-set match, wearing a sleek Nike bodysuit that garnered lots of attention.
Halep, who lost in last year's final, was playing 16th-seeded Elise Mertens.
"And then he came up with this extraordinary analysis: That you were intimidated by her supermodel good looks". Fourteen years and eighteen defeats later, Williams is still lauding it over her old rival.
Kerber has never been beyond the quarterfinals at Roland Garros and next faces top-seeded Simona Halep, last year's runner-up. But every time the players are taller, bigger, faster, stronger, but it's not only tennis players. She has lifted Coupe Suzanne Lenglen trophy on two occasions in 2012 and 2014.
Monday's scheduled match was due to take place just two days after Williams had blasted Sharapova's autobiography for being "100 percent hearsay" when it came to references about the aftermath of that 2004 Wimbledon final.