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The Australian Open champion was kept on her toes for two sets by an opponent who had beaten her in their previous encounters before strolling through the decider to set up a clash with Czech seventh seed Petra Kvitova.
Collins was bothered by abdominal pains in the third set, looking unable to give her maximum effort in the finale on court Philippe Chatrier.
"This is really special, I'm super happy. I know she plays really aggressive so I needed to have a better first serve percentage and play aggressive myself; I did a great job overall," said Kenin, who won four of her five matches at Roland Garros in three sets.
"I guess I like winning in three sets. I know it's tough but I'm getting the job done."
After a solid start on both sides, Collins served a woeful double fault to hand Kenin the first break of the match, and a 3-2 lead.
She held serve and set up another break point at 4-2 but Collins saved it to stay in contention.
Kenin was, however, solid on her service games and she bagged the opening set when her opponent's return sailed wide.
It was the first time Kenin took a set against Collins in four encounters, and the fourth seed kept her momentum, breaking again for 3-2 in the second set as her unseeded opponent smacked a forehand long.
But this time, Collins hit back to level for 3-3 and she started to threaten Kenin's serve, eventually breaking again to level.
The comeback was short-lived, though, as Collins quickly fell 4-0 behind in the decider before taking a medical timeout, holding her midriff as she went off the court for treatment.
Kenin easily won the remaining two games.
"I felt like I was kind of a little bit off with my shots. Sometimes just going for it and just wasn't working for me today," said Collins, who suffered from an abdominal injury earlier this year.
"She played well. Obviously there is a physical ailment, but I don't want that to take away from the great tennis that she was playing.
"It's nerve-racking because I have had this injury earlier in the year. So when you start feeling something like I did on the court, you get a little bit nervous because it left me out from competing for a couple of months."