World number two Swiatek was hunting a fourth title at the Foro Italico but failed to get past the third round of the last major tournament before the French Open.
Collins will now face one of Elina Svitolina or fellow American Hailey Baptiste in the last 16 as the world number 35 hunts an unlikely second WTA 1000 title after winning in Miami last year.
Swiatek’s early exit is a major shock for the Pole, who usually dominates her rivals on clay and has a hugely impressive record in the Italian capital.
The manner of her defeat is another worrying sign ahead of Roland Garros, as she was also thrashed in straight sets by Coco Gauff in the semi-finals of the Madrid Open earlier this month.
Swiatek was barely recognisable from the player who has won four French Open titles, being broken four times in the first set and failing to impose herself at all on Collins, against whom she had previously won eight of nine meetings. (AFP)
