This was only Kasatkina's second grand slam quarter-final, so she's still feeling her way in the game.
It worked. The 11th-seeded Kerber reached her second final at the All England Club by avoiding too many mistakes and using a seven-game run to seize control for a 6-3, 6-3 victory over the 12th-seeded Ostapenko on Thursday.
Meanwhile, 2017 French Open champion Ostapenko made light work of Cibulkova who hadn't previously lost a set throughout her Wimbledon campaign.
Jelena Ostapenko hardly broke sweat as she beat Slovakia's Dominika Cibulkova and moved into the Wimbledon semi-finals for the first time.
Jelena Ostapenko fired a truckload of winners against the Slovakian in the women's quarterfinal, taking her down in straight sets 7-5, 6-4 on Court No. 1 at the All England Tennis Club in London.
Williams has every reason to be confident against 13th-seeded Goerges of Germany, who is playing in her first Grand Slam semifinal.
"I knew after the first set, 'all right, let's go three sets.' I'll just keep fighting", Williams said.
"I had some great matches", she said.
Kasatkina, just 21-years-of-age, threw the kitchen sink at her more fancied opponent - her 33 winners and 31 unforced errors were proof of this. Even if I played, I was not able to compete with the knees the way I had.
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"To be here, to be in the semi-finals, I always say I plan on it, I would like to be there, have these goals".
With all top-10 seeds crashing out before the quarter-finals, Ostapenko is the second-highest ranked player still standing in the draw, behind No. 11 Angelique Kerber.
"I am OK, I feel good, I feel like I did better today, I had to", she said.
"It's Love-40 and I was not winning my serve, so I was, like, Oh, my God, I need to go there and try to talk to the chair umpire and try to ask her to ask the referee to come".
German 11th seed Angelique Kerber reached the Wimbledon semi-finals with a 6-3 7-5 win over Russian Daria Kasatkina on Tuesday but she needed seven match points to see off the 14th seed.
Kasatkina steadied herself to reach 3-4 before she double-faulted on break point and lamely surrendered the game to Kerber, who then served for the set.
Soon, she had a chance to serve for the set after playing the best return game of the match. But dropping a set against the world number 52 also showed that Williams is not at her most imperious.
That first game consisted of eight points: Three were unforced errors by Ostapenko, including a double-fault to begin the proceedings; the other five were winners by her, including a 100 miles per hour ace to close the hold.