It was an easy tie for the tennis star as she continues in her quest for a record-equalling Grand Slam singles title.
The 10th seed, chasing a first major since the 2017 Australian Open, survived the first-set fright in her opening match, but there was no hiccup this time.
She will take on fellow American Sofia Kenin in the next round, with world number one Naomi Osaka a potential opponent in the quarter-finals.
As often with Williams, both the clothes and the arm did the talking on Court Philippe Chatrier.
She stepped into the stadium wearing her Virgil Abloh-designed dress printed with the words “Reine, Mere, Champion, Deesse” (Queen, Mother, Champion, Goddess).
On the court, the 37-year-old was given a decent workout by world number 238 Nara, who was playing her only second match in the main draw of a tour-level tournament this year.
Nara stood her ground in the first seven games but derailed in the eighth as Williams broke for 5-3 with a booming forehand winner down the line.
The Japanese cracked earlier in the second set, dropping serve in the third game, and never recovered as Williams snatched her 801st victory on the tour.