Against Cirstea, Erakovic took the match to her more fancied opponent in the oppressive 41-degree temperatures. She was aggressive on the big points and held her nerve, even as she faced four set points in the second set.
"It was probably my best performance at the Australian Open so far," she said. "I knew what to expect. She hits the ball really big and I tried to dictate as much as I could. I tried to take my time with the heat and deal with it as best I could.
"I knew she was a bit nervous [at the end of the match] and was feeling it, too, and just trying to put the ball back in the court. From then on I thought, 'go on, take a chance and just go for it'.
"I wouldn't say it was my best tennis I've ever played but, mentally, I felt I really dug in and preformed at a good level."
Both players struggled to hold serve in the opening set, which saw five breaks of serve, before Erakovic closed it out when serving for the set.
The second set saw just two breaks of serve before it was decided in a tiebreaker.
Cirstea looked like she would send it into a third set when she held a handful of set points but Erakovic recovered to win the match in one of her biggest results at a grand slam.
Erakovic is also playing doubles with China's Jie Zheng and the 10th-seeded pairing will play French duo Alice Cornet and Carolina Garcia in the first round.