Nestor and Mirnyi won the trophy last year, and the 39-year-old from Toronto claimed it in 2010 with former partner Nenad Zimonjic of Serbia.
Nestor, winner of more doubles titles than any other man in the game, claimed his first trophy at Roland Garros in 2007 with Mark Knowles of the Bahamas. He and Knowles also lost the 2008 final.
Nestor and Mirnyi will face off in the Saturday final against the winner from a semi between second-seed brothers Bob and Mike Bryan of the U.S., who beat Pakistani Aisam-Ul-Haq Qureshi and Jean-Julien Rojer of the Netherlands 6-3, 7-6 (7-5).
The Nestor team won in 76 minutes with seven aces and breaks on three of 11 opportunities against the Italians, whom they defeated in an Australian Open third round meeting four months ago.
In the junior event, Vancouver’s Filip Peliwo continued his bid to become the first Canadian to win a boys title as he moved into the semifinals with a 6-4, 6-1 win over American Noah Rubin.
"We're playing well, but we have to keep our best for the final," said Nestor. "We're playing the Bryans who beat us pretty badly in Monte Carlo, we'd love to get that one back.
"But we have to play to win because that's the only way it's going to happen."
Peliwo will next face Adam Pavlasek, boyfriend of Wimbledon champion and Paris semifinalist Petra Kvitova, after the Czech beat Australian Luke Saville 6-3, 6-3.
Saville won the Australian open juniors to deny Peliwo that title in January.
Nestor and Mirnyi got off quickly against their 14th-seeded opponents, breaking Bracciali in the second game.
But the match was coloured by the fact that Nestor's team knew Bracciali was carrying an injury from a mixed doubles match the day before.
"He was hobbling around on a few shots," said Nestor. "But that's something you don't want to think of. You can start wondering about him and not thinking of your own game."
The top seeds went up a second break for 5-1 but Nestor was broken a game later after saving a pair of break points. He took the opening set two games later after 36 minutes.
The second set was interrupted for 25 minutes by a passing shower on a day which began with heavy rain and left gusting winds in its wake.
With Nestor and Mirnyi leading 3-1, the players were forced off court but returned quickly in sunny, blustery conditions.
"We may have felt the conditions a bit more when we came back out," said Nestor. "We focused on our game but we may have let some opportunities slip by.
Mirnyi finished the afternoon with a love game, firing an ace on the first of three match points.