London: Serena Williams survived a major scare before sealing her 11th Wimbledon semi-final appearance, while Angelique Kerber remains the seven-time champion's main title rival after the German joined her in the last four on Tuesday.
Williams was in danger of a stunning quarter-final exit after world number 52 Camila Giorgi became the first player in this year's tournament to take a set off the former world number one.
But Serena bludgeoned her way out of trouble, winning 3-6, 6-3, 6-4 to stay on course for an eighth All England Club triumph.
It was Serena's 100th career main draw victory on grass.
The 36-year-old will play German 13th seed Julia Goerges on Thursday for a place in Saturday's final.
"I knew after the first set, 'all right, let's go three sets'. I'll just keep fighting," Williams said.
"This is only my fourth tournament back so I don't feel pressure, I don't feel I have to win this.
"I still have a long way to go to be where I was."
Serena is the first woman to reach a Grand Slam semi-final without facing a top 40 ranked opponent since 2013.
Williams is into the 35th Grand Slam semi-final of her career and her first since winning last year's Australian Open.
Having shaken off the rust following her lengthy lay-off after the birth of her daughter Olympia in September, Williams is on the verge of a 10th Wimbledon final appearance.
Her path to the title has been wide open from early in the tournament as Garbine Muguruza, Maria Sharapova, Simona Halep, Petra Kvitova, Venus Williams, Caroline Wozniacki and Sloane Stephens have all been eliminated.
Williams, a 23-time major winner, is hoping to join a select group of women who have won Grand Slams after becoming mothers.
Goerges advanced to the Wimbledon semi-finals for the first time with a 3-6, 7-5, 6-1 win against Dutch 20th seed Kiki Bertens.
Goerges had suffered five successive opening round defeats at the All England Club before this year.
It also took her until her 42nd Grand Slam appearance to finally get through to the last four at a major.
"It is a great opportunity to play Serena here where she has won so many times and is a great champion. I think everyone here has a great chance so you have to take it," Goerges said.
With Kerber also in the last four, it is the first time two German woman have made the semi-finals of a Grand Slam since Steffi Graf and Anke Huber at the 1993 French Open.
The carnage at the top leaves 11th seed Kerber -- beaten by Serena in the 2016 Wimbledon final -- as the highest ranked player left.
Kerber takes on Latvia's Jelena Ostapenko in the other semi-final.
The 30-year-old clinched her third appearance in the Wimbledon semi-finals with a 6-3, 7-5 win over Russian 14th seed Daria Kasatkina
Kerber, who won the Australian and US Open titles in 2016, will be playing in the seventh Grand Slam semi-final of her career.
"We both played on a really high level. I was just trying to stay focused on my serve. It's great to be in the semis," Kerber said after she finally sealed the win on her seventh match point.
Ostapenko is the first Latvian woman to reach a Wimbledon semi-final as the former French Open champion beat Dominika Cibulkova 7-5, 6-4.
Just four years ago, Ostapenko was winning the junior Wimbledon title and now the youngest player left in the women's singles is only one win away from the final.
Ostapenko hasn't dropped a set in her first five matches and the 12th seed said: "I'm just enjoying being here. I'm fighting until the end and I'm gaining more confidence."