Swift, who took second to another Frenchman, Arnaud Démare, in Milan-San Remo on Saturday, got on Bouhanni's wheel in the final 100 metres of the sprint, but couldn't find the speed to come around him.
In a race bereft of top-quality sprinting, Bouhanni and Swift were the strong favourites for the first stage of the race, which featured five categorised climbs in a rolling parcours.
Team Sky came to the front for the final 15km to both set Swift up for the sprint and keep leader Chris Froome safe from any potential trouble further back.
Cofidis were also buzzing around the front, as were FDJ with Kevin Reza their preferred sprinter for the day.
Nicolas Roche went on his own out the front with 5km to go on a slight uphill ramp, causing consternation in the peloton as other teams were setting up their lead out trains.
Geoffrey Soupe led out Bouhanni in the sprint, but Bouhanni decided to leave his teammate's wheel and get behind Gerrans and Swift on the left of the road.
The move paid off as the sprinter barrelled past Swift and over the line by half a bike's length.
Volta a Catalunya stage one, Calella - Calella (175km)
1. Nacer Bouhanni (Fra) Cofidis, 4-28-51
2. Ben Swift (GBr) Team Sky, st
3. Daryl Impey (RSA) Orica-GreenEdge, st
4. Enrico Gasparotto (Ita) Wanty Groupe-Gobert, st
5. Aleksei Tcatevich (Rus) Katusha, st
6. Carlos Barbero (Esp) Caja Rural, st
7. Jordi Simon (Esp) Verva Activejet, st
8. Kevin Reze (Fra) FDJ, st
9. Eduard Prades (Esp) Caja Rural, st
10. Georg Preidler (Aut) Giant-Alpecin, st
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