Trailing the Omega Pharma-Quick Step team of Mark Cavendish by three seconds at the halfway split, Orica-GreenEdge put in a barnstorming second leg to finish the pan-flat race against the clock by 0.75 seconds.
The Australian team's time of 25 minutes and 56 seconds gave them an average speed of 57.7kmh - a record for a team time trial in any Grand Tour.
Victory put Gerrans, who won Monday’s third and final stage in Corsica, into the yellow jersey after the RadioShack-Leopard team of overnight leader Jan Bakelants finished 29 seconds down in 11th place.
The Sky team of British race favourite Chris Froome posted the third best time, three seconds behind Orica-GreenEdge, while the Saxo-Tinkoff squad of Spaniard Alberto Contador took fourth, nine seconds in arrears.
Back-to-back wins for the Australian team caps a remarkable turnaround for Orica-GreenEdge, whose team bus caused something of a flashpoint on stage one after getting wedged underneath the finish line gantry in Bastia.
Twenty-four hours after Gerrans outsprinted Peter Sagan to take stage three in Calvi, the 33-year-old secured the first yellow jersey of his career after another superb team performance from GreenEdge.
“It’s the pinnacle of the sport and I’m thrilled to take the yellow jersey - especially after such a fantastic team effort,” said Gerrans, who leads team-mates Daryl Impey and Michael Albasini on GC.
“Very few guys get to wear the yellow jersey and so it’s an honour. Everyone rode 100 per cent today - just like yesterday - and it’s great that we can get rewarded together as a team.”
To win, Orica-GreenEdge had to turn over the early target time set by Omega Pharma-Quick Step, who were the second team to roll down the ramp on a warm and sunny day on the Cote d’Azur.
With sprinter Cavendish suffering from bronchitis and powerhouse Tony Martin still recovering from his horrific injuries sustained in the pile-up that marred the conclusion of Saturday’s opening stage, OPQS’s motivation was simple: win the time trial and put their Polish youngster Michal Kwiatkowski into the yellow jersey.
A blistering ride from the Belgian team saw OPQS set a target time at the split that was not to be beaten by any team all afternoon - even GreenEdge.
Garmin-Sharp came through the split four seconds down - but hopes of seeing their man David Millar into the race lead evaporated on the Promenade des Anglais, Garmin coming home 16 seconds down on OPQS at the finish.
Saxo-Tinkoff rode through the split just one second down - and despite seeing Benjamin Noval injured by a collision with a spectator with a camera.
But Contador’s team slowed in the return leg, crossing the line eight seconds behind OPQS to end any hopes of seeing Nicolas Roche to the top of the overall standings.
Sky rode a technically strong time trial to come through the split just three seconds down at the 13km mark. Geraint Thomas, riding with a small fracture in his pelvis, contributed right until the final kilometre before peeling back, his work for the day done.
But Sky were unable to topple OPQS and put Norway’s Edvald Boasson Hagen into the yellow jersey. They came home four seconds down and it looked like the spoils would go to the Belgian team.
Orica-GreenEdge, however, put in a quite brilliant return leg to turn the tables and pip OPQS by three-quarters of a second.
“It’s an amazing team, that’s for sure. That was an incredible ride,” veteran Stuart O’Grady said moments after the finish in Nice.
“All the boys were super motivated after yesterday’s win and we rode very smoothly. If someone beats that then they deserve to win.”
O’Grady’s words rang true - and no one was able to better the second-year ProTour team.
Pipping OPQS by less than a second, Orica-GreenEdge were three seconds ahead of Sky, nine seconds better than Saxo-Tinkoff and 17 seconds clear of both Lotto Belisol and Garmin-Sharp.
The BMC team of Cadel Evans and Tejay van Garderen recorded the ninth best time, 26 seconds behind Orica-GreenEdge.
Spaniard Alejandro Valverde is well poised on GC after his Movistar team came home just 20 seconds down, while compatriot Joaquim Rodriguez will be happy that Katusha only conceded 28 seconds.
Things were less positive for polka dot jersey Pierre Rolland, who lost more than a minute to his rivals after Europcar came home 1:13 down in 19th place.
Gerrans tops the overall standings, level on time with team-mates Impey and Albasini. OPQS youngster Kwiatkowski, the race’s white jersey, is fourth, one second down and level on time with fifth-place team-mate Sylvain Chavanel.
Sky trio Boasson Hagen, Froome and Richie Porte are three seconds in arrears in sixth, seventh and eighth respectively.
Saxo-Tinkoff’s Roche is nine seconds down in ninth place, level on time with team-mates Roman Kreuziger, Michael Rogers and Contador.
Wednesday’s stage five is a 219km undulating ride through Provence from Cagnes-sur-Mer to Marseille which should conclude with a bunch sprint between the peloton’s fast men. Time will tell is Britain’s Cavendish can shake off his illness and open up his account in the 100th edition of the world’s greatest bike race.