"It was not so easy (playing Petkovic)," said Kerber after the match. "We’ve known each other forever. It's always tough to play against a friend."
Fourth seed Simona Halep also won emphatically, 6-4 6-1 over Donna Vekic.
Halep, the 2015 champion, broke her Croatian opponent no fewer than seven times.
"My serve is not that big but I like to return. I’m really proud of it," Romanian Halep said.
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"I’m not very powerful but I have a little bit the technique and the angles. I love this place. I have great results here."
While Kerber and Halep won in quick fashion, American 12th seed Venus Williams beat Serbian Jelena Jankovic in a dramatic battle between former world number ones.
Jankovic raced through the first set and seemed poised for an upset, but the second set tiebreak proved pivotal, as Williams survived, staving off three match points en route to a 1-6 7-6(5) 6-1 victory.
"It ain't over til' it's over, and I didn't see no fat lady singing," said Williams, who played with her left thigh heavily strapped.
Another American, ninth seed Madison Keys, made a winning return in her 2017 debut, triumphing 6-1 7-5 over Mariana Duque-Marino of Colombia.
Keys missed the Australian Open in January while recovering from wrist surgery.
"It felt really good," Keys said. "I really, really missed competing and being able to go out there and get a win on top of it was amazing."
Former world number one Caroline Wozniacki also advanced, the 13th seeded Dane turning back qualifier Magda Linette of Poland 6-3 6-0.
(Reporting by Gene Cherry in Salvo, North Carolina; Additional reporting by Andrew Both; editing by Pritha Sarkar/Amlan Chakraborty)
