"I don't know what I did", Williams said in a post-game press conference.
The seven-time champion dropped her first set of the tournament to Italy's Camila Giorgi but came through 3-6, 6-3, 6-4 to reach the semi-finals for the 11th time.
The match that precedes Williams on Centre Court promises to be more competitive.
It's not as if Serena needs much encouragement to dominate at Wimbledon, where she has already reached nine finals. The two met last month in the second round at the French Open, with Williams winning in straight sets.
It is the third time Kerber has reached the last four at Wimbledon, where she was runner-up in 2016.
The American then cruised through the deciding set with a single break of serve enough to ensure her place in the semi-finals.
She now has a 39-35 record when losing the first set at a major.
World No 52 Giorgi blasted 20 winners and really took it to Williams, taking the first set thanks to one break, in the sixth game.
Looking to become the first Italian woman to make the Wimbledon semifinals, Giorgi did not let up, even when the match started to look like it was slipping away.
"Everybody has to deserve that, I think". "In this tournament, she seems to be in the right mood".
"I feel like I'm getting to where I want to be".
It's okay, Serena, just keep your eyes on the prize at Wimbledon! "I feel like I'm back, but I still have a long way to go to get to where I was".
In the last men's quarterfinal, which was suspended because of darkness after the third set Monday night, 2009 US Open champion Juan Martin del Potro defeated Gilles Simon of France, 7-6 (7-1), 7-6 (7-5), 5-7, 7-6 (7-5). Suddenly, Williams looks as great as the eight Wimbledon titles suggest she is.
Serena Williams returns a shot to Evgeniya Rodina.
The Canadian rapper, 31, couldn't help but smile as he showed up to another of the icon's grand slam tennis matches, with the star vying for her 24th single Grand Slam title, and her first since welcoming baby daughter Alexis in September.
Williams, for the first time since her comeback, appears to have her body and mind aligned to take that next step.