Sometimes I feel I can fight. "I was just trying to go for the shots when I had to", Ostapenko said.
"I hope he's going to go even further in the tournament".
Williams got the better of Kerber in the 2016 final, beating the German 7-5, 6-3 to earn her seventh Wimbledon title. "In this tournament, she seems to be in the right mood". "Stay tuned for the next episode, Serena Williams Centre Court".
Cibulkova did her best to hang on but was left chasing shadows as Ostapenko blasted a backhand victor on her first match point to become the only woman to reach the semis without dropping a set in this year's tournament.
Kerber, the former No. 1 and two-time major champion who was the runner-up at Wimbledon two years ago, took advantage of Kasatkina's erratic serving and many errors to return to the last four.
Hsieh argued, correctly, for several minutes that the point should be replayed but the umpire would not budge, being heard to say she could not remember if Hsieh's shot had gone in.
Kerber takes on Latvia's Jelena Ostapenko in the other semi-final.
With only two more matches to go to become the third woman to win the girl's and ladies titles at Wimbledon, Ostapenko will take on Angelique Kerber in Thursday's semifinal match-up.
Cibulkova has won both of their previous matchups, but she isn't going to be focused on anything but what she has to do to reach her first Wimbledon semifinal: "I played her couple of times".
"We both played on a really high level".
"I'm here just to prove I'm back, and I feel like I'm back".
Germany's Angelique Kerber celebrates winning her quarter final match against Russia's Daria Kasatkina.
Kerber, the highest-ranked player left in the tournament, needed seven match points to see off the tenacious 21-year-old 6-3 7-5.
Kasatkina made an encouraging start, putting away a forehand victor to earn a break point in the first game, but Kerber escaped with a battling hold and the 14th seed gifted her a 2-0 lead after double-faulting twice in a nervy first service game.
In a match suspended from Monday night due to darkness with the Argentine star two sets to one ahead, Del Potro sealed victory on a fifth match point after nearly four and a half hours of action on Court Two. Kerber found herself on match point six times before she finally broke through.
Del Potro looked flat as he was broken to trail 3-1 but he clawed his way back to lead 5-4 with his serve to come.
The match reached flash point when Cibulkova's return in the 10th game was called out and then corrected before Hseih's forehand landed back in play. But the match turned a game later.
Del Potro has never beat Nadal on grass and has lost 10 of their 15 encounters.