Gerrans (Orica-GreenEDGE) held a nine-second lead on compatriot Richie Porte (BMC) going into the last stage and had a well protected run in to the finish by his team mates.
The result left the general classification unchanged with Gerrans and Porte followed by Sergio Henao of Team Sky, who also claimed the polka dot jersey as the best climber troughout the six-stage event.
"We had a dream run this race, with Caleb bookending the race with a first and the last-stage win," he said.
"Overall, I think we got the sprint jersey, so I don't think we could ask for a heck of a lot more than that.
"I couldn't have asked for any more of the guys this week.
"Today, they just kept me up the front out of trouble, and we tried to give Caleb the best run for the line that we could. They really did a sensational job."
Ewan bookended his opening stage Tour Down Under with another sprint victory, this time in the streets of Adelaide, ahead of Mark Renshaw (Dimension Data) and Giacomo Nizzolo (Trek-Segafredo).
— Tour Down Under (@tourdownunder) January 24, 2016
Early chopping and changing eventually led to Thomas De Gent (Lotto-Soudal) and Maarten Tjallingii (LottoNL-Jumbo) making the break that counted.
But the exploits of the pair ended with four laps to go as De Gendt was caught after claiming a KOM intermediate sprint while Tjallingii kicked on, this time with Astana’s Lieuwe Westra on his wheel after bridging across.
But the last ditch effort by the new pairing was ultimately doomed to fail as the sprint trains ramped up the speed in preparation for the sprint.
Once the peloton hit the final 100 metres it was all Ewan, the 21-year-old demonstrating again that he was the fastest man in the field.
"The team showed this week that they're the strongest," Ewan said. "It was always going to be hard going into the race with two ambitions, trying to win sprint stages and overall GC with Simon.
"But I think we did it perfectly. We came away with four stage wins and overall."