Stewart, from Tasmania and a former junior time trial world champion, had just returned to the professional peloton to make her debut with Wiggle High5 at the four-day race.
Her teammate Nettie Edmondson won the stage that ended in a cagey bunch sprint in Gumeracha. Edmondson described the sprint as ‘messy’ but said that her teammates including Stewart got her into position to win.
"Rachele [Barbieri] found me coming into the finish and put me in a really good position," Edmondson said. "And then I found Macey [Stewart] as well and she finished off the last bit, putting me into the UniSA lead out train.
"We did what we could in the messy situation, and I jumped on the train. Then with about 400m to go we took the last corner and I tried to be patient. Lauretta Hanson kicked with about 200m to go, but I left my run really late because of the headwind and, sure enough, timed it perfectly!"
Edmondson won the sprint ahead of former two-time world champion Giorgia Bronzini (Cylance) and Lauretta Hanson (Aus) UniSA-Australia.
The crash happened a mere 300 metres from the finish line. Stewart was one of the first to go down. A medical update from the organisers confirmed she had a concussion. She wasn't the only rider to sustain injuries.
New Zealand's Sharlotte Lucas (Specialized Women's Racing) underwent precautionary x-rays and will be reassessed on Friday morning to determine if she continues in the race.