Serena Williams stayed on course for an eighth Wimbledon title with a straight-sets win over Evgeniya Rodina but said the trophy was far from being wrapped up.
The 36-year-old is playing only her fourth tournament since giving birth to daughter Olympia in September.
But with the top 10 seeds having all been knocked out, Williams is hot favourite to be crowned champion yet again on Saturday.
She was too strong for Russian Rodina, a mother herself with a five-year-old daughter called Anna, and won 6-2 6-2 in just over an hour.
Williams said: "I have a long way to go. I'm only in the quarter-finals. It's not about wrapping up a win. It's like all the other women that are still in the draw.
"Each of us, seeded or not, we're just here to do our best."
Another potential obstacle in her path to the final was cleared when Karolina Pliskova crashed out.
Pliskova was the only player of the top 10 seeds in the women's draw to make it into the second week.
However, the Czech seventh seed only lasted until Monday lunchtime, going down 6-3 7-6 (7/1) in the fourth round to Kiki Bertens from Holland.
Williams will face Italian world number 52 Camila Giorgi in the last eight, with the winner going on to face either Bertens or Germany's Julia Goerges in the semi-finals.
Nine-time Wimbledon champion and BBC summariser Martina Navratilova said of Williams: "The seas have parted for her."
Williams may have been seeded 25th despite slipping down the rankings as a result of maternity leave, but her current position of 181st in the world makes the American the lowest-ranked Wimbledon quarter-finalist in the open era.
Prior to the championships Dominika Cibulkova was unhappy that the decision to seed Williams meant she was bumped out of the top 32.
But she was even angrier with chair umpire Zhang Juan during her win over Hsieh Su-wei after having a return called out and then corrected.
Hsieh had hit the ball back into play but chair umpire Zhang awarded the
point to Cibulkova, prompting an understandable protest from the Taiwanese
player who insisted: "I put the ball in."
Yet Cibulkova argued the point should have been hers as the umpire should not change her mind.
As both players pleaded their case the match referee had to be called before, following a 10-minute delay, the umpire's decision was changed and the point replayed.
Cibulkova, who went on to win 6-4 6-1, said afterwards: "It was ridiculous. It never happened to me in my career.
"Sometimes I'm also complaining because I think it was a wrong call. But it
never happened to me that the umpire changed the decision. I think it was a
really bad decision from the supervisor and from the umpire."
The incident raised questions about Cibulkova's conduct but Hsieh said: "I understand. She's a fighter. She fights for every point. I understand she wants to win."
Cibulkova will face Jelena Ostapenko after the Latvian, last year's French Open winner, beat Aliaksandra Sasnovich 7-7 (7/4) 6-0.
Angelique Kerber is now the highest-ranked player left in the tournament.
The 11th seed, who reached the final in 2016, beat Belinda Bencic of
Switzerland 6-3 7-6 (7/5) and on Tuesday will meet Daria Kasatkina, who ended Alison Van Uytvanck's run with a 6-7 (6/8) 6-3 6-2 win.
Giorgi was a 6-3 6-4 winner against Ekaterina Makarova and Goerges beat Donna Vekic 6-3 6-2.