It was the fourth time in as many matches that Kerber had got the better of her compatriot, who is ranked 14th in the world and considered as one of the rising stars of the game.
"She is a great player who is also a good friend, so it's not easy playing against her," Kerber, who won the Paris Indoors last week, said after her 4-6, 6-4, 6-1 victory.
"We travel together and live in the same hotels, but I was focused on my game," Kerber added.
Kerber's form has been nothing short of spectacular recently, the German reaching at least the semis in six of the past 10 tournaments she played before winning her first WTA title in Paris where she beat Frenchwoman Marion Bartoli in the final.
"I am really playing well, but this is a big tournament with many stars playing, but I will really try my best," said the world's 22-ranked player.
The top eight players in the field have been given first round byes and will see action only on Wednesday, with world number one Victoria Azarenka of Belarus and Caroline Wozniacki of Denmark the favourites.
