US Open - Keothavong wins just two games in Kerber loss
The Londoner enjoyed a bright start as she secured a break point in the first game but she could not convert that and things started to go wrong quickly.
The British number two was swept out of the tournament in just 54 minutes with Kerber winning more than double the amount of points than Keothavong, 55 to 26.
In better news for Britain, Australian-born Johanna Konta, who has represented Britain since being granted citizenship in May, did make the second round after beating Hungary's Timea Babos.
It is Konta's first ever Grand Slam main draw win.