Keys recorded her first victory over a world number one in Cincinnati on Thursday, defeating Swiatek 6-3, 6-4.
Having already lost a set and going 5-0 down in the second, the writing was on the wall for the Polish star.
But Swiatek was stubborn, saving two match points to battle back to 5-4.
Keys, however, managed to reset and crush two groundstroke winners to wrap up proceedings.
"I obviously have not had the best success against World No. 1s, so being able to get a win against Iga, especially after having two losses to her already, means a lot to me, and I think I'm playing some pretty good tennis," said the American afterwards, as per wtatennis.com.
Waiting for Keys in the quarter-finals is Elina Rybakina, who defeated local hopeful Alison Riske 6-2, 6-4 earlier in the day.
Meanwhile, reigning US Open champion Raducanu's seemingly red-hot form came to an abrupt halt against world number eight Jessica Pegula, who defeated the Brit 7-5, 6-4.
Pegula is set to face Frenchwomen Caroline Garcia in the last eight.
Raducanu defeated soon-to-retire 23-time grand slam champion Serena Williams and former world number one Vicotria Azarenka this week, but came unstuck against the feisty American.
Nonetheless, the British number one is treating the tumultuous week as a learning experience.
"In the past year, I think it's probably the first tournament or one of the few tournaments that I have actually started going for my shots more," said the 19-year-old.
"I think that recently I was kind of playing and hoping they would miss, and I think I was pushing the ball around a lot more.
"This week I kind of just was like, 'Look, I'm just going to try. I don't care if I make errors, it's fine,' but I'm just going to like overhit if anything.
"To play back-to-back days between the first and second, it was pretty quick turnover.
"I think that it's difficult as well to stay mentally focused, to keep mentally just going back out there and backing the performances up."