The American powered past Alize Cornet in the quarter-final, winning the match 7-5 6-1 inside 90 minutes.
The 28-year-old previously reached the last four stage of this Grand Slam back in 2019 as she lost to Petra Kvitova in three sets.
This time round, Collins will battle Poland's Iga Swiatek for a place in the final after the 20-year-old got the better of Kaia Kanepi.
Collins, who has only dropped two sets in the tournament, said: "I feel pretty good right now. Had a good match today and I've had some great matches along the way [in] this tournament. Just really happy about how I'm feeling mentally and physically. Hopefully we can keep it going."
The American stepped away from the WTA Tour last year in order to have surgery. The player was diagnosed with Endometriosis, which is a condition where cells - which naturally line the womb - grow in other areas of the body.
Collins admitted that surgery and medication have helped to ease painful periods; something which has allowed her to train on a more consistent basis.
She added: "I think aside from surgery, I've got a lot physically stronger over the last couple of years. My strength and conditioning and my fitness has been one of the most important areas of my training and focus. I think that has transferred over to my tennis, the way that I'm able to play physically.
"With my serving, I think my serving has got a lot stronger. I think my stamina on court has improved tremendously, and I think just overall power and speed has improved, and that's something I focus so much on over the last couple of years. That's probably the biggest difference to where I was [in 2019]."
Collins also paid homage to her family for their years of sacrifice during her early years in the sport.
The American said: "I think the thing that's most gratifying is the amount of work over such a long period of time coming together. Because it's not something that happens over a year or two years, it starts from the time you're a kid and all the hard work you put in.
"I think the most gratifying part of it all is thinking back to how many early mornings my dad got up with me to go practise with me before I went to school and get in the car. I remember one time dad had a cold, and he didn't want to get up out of bed, and I cried. I said 'please, I want to go to practise, at least go for a run or something'.
"I remember him getting on the bike and accompanying me on my run when he didn't feel well so being able to share those moments with my parents and just thinking back on all the hard work they allowed me to do.
"They were the ones the drove me to practise, they were the ones that tried to provide me with the best resources in the area and get me in with the best coaches and players. I can't tell you how many hours a day they used to drive just trying to get me from one place to another so I could get everything I needed. That's probably the most gratifying part."