Williams, a 23-time Grand Slam victor and a former champion in Cincinnati, needed just 65 minutes to dispatch Gavrilova.
Following the thumping by Konta, the 36-year-old American, runner-up at this year's Wimbledon, withdrew from last week's Rogers Cup in Canada for "personal reasons".
The 20-time major victor skipped Toronto last week to pace himself with the tournament at Flushing Meadows followed by the Laver Cup in Chicago in mid-September. She has dealt with blood clots and recently said she has been struggling with postpartum emotions.
"You've got to be able to go back-to-back", said Williams, a two-time Cincinnati champion. "I just began. I just started - definitely at the very, very beginning".
"I'm just going to continue to work hard, and hopefully I'll start winning more matches". You know, there is only so much you can do before you have to get surgery or something like that. I wish I could play everything but it's not possible.
Tennis fans are furiously debating the pros and cons of best-of-five sets tennis and numerous game's top stars are having their say.
"I'm more relaxed about my schedule now".
France's Mladenovic had earlier defeated qualifier Viktoria Kuzmova 6-3 6-0, while her sixth seeded compatriot Caroline Garcia defeated fellow power hitter Victoria Azarenka 6-4 7-5 to advance to the third round.
Denis Shapovalov also reached the third round with an upset, knocking off 14th-seeded Kyle Edmund, 6-4, 7-5. Sock has lost eight straight matches since winning in Rome on 13 May. Milos Raonic, a two-time Cincinnati semi-finalist, advanced with a 6-3, 6-3 win over the qualifier Dusan Lajovic.
Djokovic, who needs the Cincinnati title to complete his collection of ATP World Tour Masters 1000 trophies, rallied to defeat Frenchman Adrian Mannarino 4-6 6-2 6-1. Ashleigh Barty stopped wild card Marketa Vondrousova 6-3, 7-5.
Greece's Maria Sakkari edged 20-year-old Naomi Osaka in a closely contested second-set tiebreak to dispatch the Japanese 6-3 7-6 (8) in their first-round match.
But it was not enough to cope with an in-form Kvitova, who emerged a 6-3, 2-6, 6-3 victor after an entertaining struggle that lasted two hours on the outdoor hard courts of the Lindner Family Tennis Center.