The 21-year-old was lying in 15th place after her first two throws but managed to produce a launch of 71.98m with her final throw.
Although it wasn't quite the 73m required to automatically qualify for Friday's final, it was still way clear of her own national record.
Speaking to BBC Sport afterwards, Hitchon said: "I was in great shape when I came in, I knew it.
"I knew [a big throw] was there and I only had one left, it was all or nothing."
Hitchon's throw put her in fifth place in Group A and she will now look for the second group not to perform better if she is to reach the Olympic final.
"I can't wait to be in the final, I've just got to cross my fingers and hope the other pool isn't further," she added.
The final gets underway at around 7.30pm on Friday evening.