Collins recorded a 7-5 6-0 victory over the 2016 Olympic gold medalist, who hasn't played a competitive match since 2020 due to injury. Puig had only played four matches since an elbow surgery in 2019, and was sidelined for more than a year and a half after that as she underwent two more surgeries, on her shoulder and biceps tendon.
Nonetheless, the former World No.27 was competitive with Collins in the opening set, before eventually falling to the American.
"You never know what to expect when someone's been out for a while, and they've been working on some things," said Collins. "You don't know what type of game style that they're going to play, so it was a little bit tricky trying to anticipate what she was going to do.
"I think she played at a super-high level, especially in the first set, and gave me a lot of challenges, so I really needed to just find my rhythm on the court."
The sixth seed has also been dealing with injuries since her incredible run at Melbourne Park, during which she had only played six matches due to a lingering neck issue.
"When you go a little period where you aren't playing some matches, you almost feel a little bit rusty," she said. "I just needed to be patient and try to get myself back into it."
Collins will face 2019 US Open champion Bianca Andreescu in the second round.