The Australian beat BMC Racing's Greg Van Avermaet to the title after the pair had attacked 4km from the finish.
Pre-race favourite Peter Sagan tried to chase them down but faded with 300 metres to go and finished well in the peloton.
Movistar's Rui Costa came in third at the head of the chasing pack, four seconds behind the winner.
“There are quite a few races that suit me at this time of year,” Gerrans said. “I have put a lot of emphasis to do well at this time of year.
“It was pretty nerve wracking. Both Greg and I worked had to build that gap and we couldn’t really slow down.
"We had one of the best riders in the peloton chasing us, Peter Sagan. It could have gone either way and I’m glad it went my way."