Pineau, who rides for the Quickstep team, covered the mostly flat 162-kilometer (101-mile) route from Novara to Novi Ligure in 3 hours, 45 minutes, 59 seconds.

“Three weeks ago I wasn't even thinking about coming to the giro, but Quickstep believed in me and now this is the greatest victory of my career,” Pineau said.

Another Frenchman, Julien Fouchard, finished second, and Yukiya Arashiro of Japan crossed third.

All three riders broke away from the main pack shortly after the stage started, and they worked well enough together to throw off the calculations of the chasing sprinters' teams.

The main pack had the three breakaway riders within their grasp on the final kilometer but couldn't close the gap, leaving American sprinter Tyler Farrar to cross fourth at the front of the group, 4 seconds behind.

Nibali maintained a 13-second lead over Liquigas teammate Ivan Basso, and became the first rider to wear the overall leader's pink jersey two days in a row.

“I hope that's a good sign I'll wear it over the next few days, too,” Nibali said.

Friday's sixth stage of 172 kilometers (107 miles) from Fidenza to Marina di Carrara includes a few short climbs.

The race's first serious climb comes Sunday with an uphill finish to Terminillo in central Italy.

The race ends May 30 in Verona.