The Pole came into Thursday's (AEST) last eight match having won her last 22 sets at Roland Garros, but lost 6-4 6-4 to the competition's 17th seed.
Swiatek headed to Paris full of confidence after winning on clay in Rome two weeks prior, and she had also helped Bethanie Mattek-Sands into the semi-finals of this year's doubles.
However, the world number nine believes she may have paid the price for all that tennis in the form of a lacklustre display against Sakkari.
She said: "Well, obviously I didn't play my best tennis. That's for sure. But Maria did a good job with playing at my forehand, which wasn't working pretty well today.
"It's good for her that she saw that. She picked good tactics, for sure. I struggled with picking the right place where to play. I couldn't play some shots that usually give me points.
"Yeah, my balls weren't, like, really deep and heavy. Basically that's my biggest weapon, so it was really hard to play without that.
"Also, you know, I think, like, past couple weeks hit me kind of yesterday. I just didn't have good days, I couldn't do like physical recovery well because I was stressed. Days like that happen, and it's normal."
Swiatek left the court for treatment on her thigh after losing the first set, but she refused to blame that issue for her defeat.
She added: "Right now I know it's nothing serious. When I was on court, I felt it totally differently. As I said, I couldn't even sleep well yesterday. I slept like a few hours.
"I think I was feeling everything twice as much as I should. It was hard to rationally just see what's going on. I made the decision to tape it just to feel sure [to give] me, like, a little bit more confidence when I was moving.
"Still my reaction was bad. I didn't play well, like, tactically and also technically. I was on my heels, so it's hard to make something of that kind of game."
Sakkari, meanwhile, revealed that her commitment to simply enjoying Wednesday's match helped her secure a maiden Grand Slam semi-final berth.
She said: "I'm speechless - it is a dream come true. It is a very nice feeling, I couldn't have done it without my team and their support so I want to thank them.
"We still have a long way to go of course [if we want to win the tournament] but we made a huge step.
"I'm not going to tell you the game plan of course because we will play again [against Swiatek] for sure! So I'm not gonna say our little secrets!
"But I really enjoyed it. Before coming into the match I just sat down and spoke to myself and said it is a very important match but just enjoy it - playing at one of the best stadiums in the world. So I have enjoyed it."
Greece boasts two semi-finalists in this year's French Open after Stefanos Tsitsipas also progressed to the last four of the men's draw.
And Sakkari believes the sport may even have overtaken football and basketball in terms of popularity back in her homeland.
She said: "Now it's probably the biggest sport these days. Football is over. Basketball is over. So tennis is in the spotlight.
"Yeah, with Stefanos, I mean, we're very close. We know each other since a very young age. I mean, I see him every day here. We're actually having dinner with our teams next to each other every night.
"I'm very, very happy for him and his family. It's very exciting times for Greek tennis."