The Czech 31st seed kept her composure from the back of the court to force her opponent into 35 unforced errors across the match as Ostapenko's bid for a second Grand Slam title since her first in 2017 unravelled on Court One which, on a rare occasion this tournament, had its roof open.
She will face 2022 Wimbledon champion Elena Rybakina in the semi-finals.
Ostapenko had power in her serve but struggled to place it, landing less than 50% of her first serve during the opening set. Krejcikova, French Open champion in 2021, broke in the third game and went on to clinch the opener.
Ostapenko rallied to break her opponent in the second set and open a 4-1 lead. However, mistakes once again dogged her game and Krejcikova put together a run of four winning games to go 5-4 up.
The match went to a tiebreak and a brilliant crosscourt forehand from Krejcikova found the far line to give her a mini-break from which she went on to close out the match, sealing her first win over the Latvian in their four most recent encounters.
"I don't have any words right now. Just a minute ago, I told myself that I'm going to leave here everything I have and I'm really happy that I did and yeah, it's a great moment for me," Krejcikova said on court.
"It's an unbelievable moment that I'm experiencing right now in my tennis career."
That Krejcikova has won five consecutive matches on grass for the first time in her career is all the more remarkable given she only had three wins on the Tour from February to June this year as she recovered from illness.
"It was a very, very difficult period. It was actually super difficult even before this tournament. I really want to thank my team that is there today," she added.
"There have been many doubts from inside but also from the outside world, but I'm super happy that I never give up and that I'm standing here right now and that I qualified to be in the semi-finals."