Swiatek held a commanding 7-1 head-to-head record against Collins before Saturday's contest and yet another early defeat does not bode well for the 23-year-old, who has not won a tournament since her fourth triumph at Roland Garros last year.
Swiatek has now lost nine matches this year - as many as in all of 2024 - while she has not reached a clay-court final ahead of her bid to retain the French Open title later this month.
"It hasn't been easy," she told reporters. "For sure, I'm doing something wrong. So I need to just regroup and change some stuff. I had some advice from the team, I'll just try to do this.
"I think I just wasn't there, present, to fight and to compete (against Collins). I focused on mistakes. It's my mistake and I'm not doing things right. So the focus is on the wrong things from my side and I'll try to change that.
"I'm not able to play my game. I'll just try to change my mindset a little bit."
For Collins, though, it was a huge breakthrough.
"I played against Iga so many times ... When you play that many close matches and get this close and also play some of your best tennis and lose, I think you learn a lot," she said.
"I feel like I applied that today."
Five-times grand slam champion Swiatek went 5-0 down in the opening set before getting on the board to avoid a bagel.
Collins was lethal from the baseline, mixing it up with forehand and backhand service return winners as she picked apart Swiatek's serve in an opening set that was one-way traffic.
The second was level at 4-4 as Swiatek showed flashes of brilliance, but 31-year-old 2022 Australian Open runner-up Collins showed no mercy, sealing victory in one hour and 44 minutes when a return went wide.
Collins fired 32 winners and converted six of eight break points while Swiatek, who had won the tournament three times in the last four years, made 22 unforced errors.
