Afterwards, she announced that she would not be participating in the Olympic Games due to the heavy load on the game.
The 33-year-old was even discussed as the German flag bearer at the opening ceremony in Tokyo.
In the round of 32 on Wednesday, Kerber will face number four seeded Ukrainian Elena Svitolina, who won the bronze medal in Tokyo.
The tournament in Cincinnati is top-class, including world number one Barty and Japanese star player Naomi Osaka.
Great start: This is how Kerber beat French Open semi-finalist Sakkari
World class counterattack: Medvedev shows Opelka the limits in the final
