Sharapova needed just 66 minutes to see off 12th-seeded Kasatkina in an impressive and timely display of big-hitting with the US Open getting underway in just under three weeks' time.
Two-time Cincinnati champion Serena lost the Wimbledon final to Angelique Kerber last month.
Maria Sharapova insists she is not finished as a Grand Slam force despite her worst ever performance at Wimbledon.
Sharapova, the 2004 champion, was joined at the exit by 2011 and 2014 winner Petra Kvitova who was stunned by Belarusian world number 50 Aliaksandra Sasnovich.
Maria Sharapova, the 2004 Wimbledon champion and five-time major winner, returns to the tournament for the first time since 2015.
Serena, 36, missed Wimbledon last year while preparing to give birth and has endured a rocky time since resuming her career earlier this year.
Seven-time Wimbledon champion Serena Williams has been seeded 25 for this year's women's singles by the organisers despite being ranked 183 in the world.
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.
Sharapova, who missed the 2016 tournament because of a doping ban and last year after she was refused a wild card, was broken six times, committed 27 unforced errors and won just five points on her own serve in the second set.
The 36-year-old said she had suffered a pectoral muscle injury in her third-round win over Julia Goerges and "can't serve at all".
Serena Williams said she had suffered a pectoral muscle injury in her third-round win over Julia Goerges and "can't serve at all".
Maria Sharapova's last win over Serena Williams came at the 2004 WTA Tour Championships -- before even the birth of Twitter and YouTube.
Sharapova and Serena have met 21 times, with the American leading the head-to-head record 19-2 after 18 consecutive wins dating back to 2004.
Former champion Garbine Muguruza reached the French Open last 16 with a comfortable 6-0, 6-2 win over Australia's Sam Stosur
Maria Sharapova will return to the showpiece Court Philippe Chatrier for the first time while Rafael Nadal defends his 15-0 record over Richard Gasquet.
Highly-rated Canadian teenager Denis Shapovalov was knocked out by Germany's Maximilian Marterer 5-7, 7-6 (7/4), 7-5, 6-4.
The top seeded Rafael Nadal, bidding for an 11th title and his 17th major, next faces Argentina's Guido Pella for a place in the last 32.
Former world number one Williams, now ranked a lowly 453, is playing a Grand Slam for the first time since she won her 23rd major at the 2017 Australian Open after which she stepped off the tour to give birth to her daughter in September.