The Australian outfit, which made its race debut last year, picked up their first Tour de France stage win thanks to Gerrans when he pipped Peter Sagan at the finish line in Calvi on Monday.
Orica's triumphant ride over a mainly flat course around Nice pushed Omega-Pharma off the virtual leaderboard by just one second.
Gerrans now leads teammate Daryl Impey by one second in the general classification ahead of Wednesday's fifth stage.
"We weren't the favourites for this course but we went out and gave it everything we had," said Gerrans.
"On this team we're all good friends and we work hard to help each other.
"It's unbelievable. It's been a dream two days for us. It really doesn't get any better than this."
Despite having no yellow jersey contender in their nine-man team Orica-GreenEdge were overjoyed at a prestigious collective win which means Gerrans will wear yellow into Wednesday's stage from Cagnes-sur-Mer to Marseille.
With no time bonuses on offer at the end of each day's stage, the former Australian champion could also realistically keep the race lead until the start of two Pyrenean stages beginning Saturday.
Omega-Pharma had set the early pace in a time of 25min 57sec thanks in large part to the talents of Germany's world champion in the discipline, Tony Martin.
A win for the Belgian outfit would have put young Pole Michal Kwiatkowski into the yellow jersey and helped make amends for Mark Cavendish's failure to win the sprinter-friendly opening stage on Corsica.
However despite the high hopes the Belgian outfit was pushed into second by Orica's winning time of 25:56.
The Sky team of overall race favourite Chris Froome finished third on the stage at 3secs off the winning pace, with his yellow jersey rival Alberto Contador coming over the finish with his Saxo Bank team a further six seconds off the pace.
Froome said Sky had been happy to finish high up without taking the lead of the race, that would have forced them into using precious energy protecting the yellow jersey.
"The main objective of today was to come through without having lost any time on the big contenders, but we've actually come through it having gained a bit of time. So that's a fantastic thing," said the Kenyan-born Briton.
Despite losing six seconds to Froome, Contador was buoyed by a team performance which he said has given him assurances about his form.
"I think it was a good day for us. Of course it's always better if you finish in front of all your rivals, but if you look at the GC we are in contention," said the Spaniard.
"I'm very happy because the team gave 100 percent. We are only four stages in, and I'm getting better every day. My aim is to be in perfect condition for the Pyrenees."
Garmin had hoped for the stage win that would have given David Millar the yellow jersey, 13 years after the big Scot wore it for the first time thanks to his victory in the prologue at the 2000 Tour.
But Millar admitted his personal performance in the race against the clock may have been decisive in leaving them with a 16-sec deficit to virtual leaders Omega-Pharma that he said "may as well be light years".
"I wasn't on a good day, and that lost us some time. But we were beaten fair and square so we can't be too hard on ourselves," said Millar, who admitted his disappointment at not taking the yellow jersey.
"It was really hard not to have it in my mind beforehand. I'm very disappointed to be honest."