The loss made this the first year in Williams’ pro career, which began in 1997, that she has not gone past the second round in any Grand Slam tournament. “Losing a match like this isn’t a lot of fun, but that’s sport,” Williams said.
Williams missed a chance to avenge a third-round loss to Kerber at the London Olympics.
Meanwhile, Serena Williams registered a 6-2, 6-4 win over Spain’s Maria Jose Martinez Sanchez to book a spot in the third round.
Serbia’s Ana Ivanovic also reached the third round with a 6-2, 6-2 win over Sofia Arvidsson of Sweden.
Second seed Agnieszka Radwanska almost suffered a fourth successive second-round exit before fighting back from a set and 3-1 down to beat Spain’s Carla Suarez-Navarro 4-6, 6-3, 6-0.
In the men’s event, French fifth seed Jo-Wilfried Tsonga crashed out to his worst Grand Slam showing in more than five years with a second-round 6-4, 1-6, 6-1, 6-3 defeat at the hands of unheralded Martin Klizan.