Apart from the opening couple of games, 28-year-old Keothavong struggled to match her German opponent, who is currently ranked sixth in the WTA standings.
"Where we both are in terms of confidence and our games I think reflected the outcome of the match today," the Brit told reporters. "I just made too many errors and she's someone who doesn't miss much."
Today's defeat had led some pundits to question Keothavong's future in the sport, with some claiming that the time is right for her to make way for some of her younger compatriots.
However, the Hackney-born player has insisted that she has no intention of calling time on her career.
"It's not easy losing all the time but I still enjoy what I do and want to keep going," he added. "I don't cry myself to sleep every night, that's for sure. I will never have this time again."
Keothavong has never gone beyond round three of a Grand Slam since turning professional at the age of 14.