The Italian has faced growing questions about his ability to rediscover his previous prowess since his switch from Yamaha to Ducati, particularly when he was comfortably outpaced by team-mate Nicky Hayden in the 2012 season-opener in Qatar.
Rossi however says that he still believes he can challenge at the front, and was therefore pleased to seize the opportunity presented to him by a wet Le Mans circuit.
"I've heard many things about me lately, [and] honestly it pissed me off," Rossi told Gazzetta dello Sport. "It's as if I'm old at 33, but I'm not. I feel in shape and I've had the chance to demonstrate it."
The seven-time champion added that triumphing over Casey Stoner during the pair's late battle in France was almost more rewarding than securing his best ever finish for Ducati.
Rossi has enjoyed a strained, and at times acrimonious, relationship with Stoner ever since the pair went toe-to-toe for the 2007 title.
They staged one of the defining races of recent years at Laguna Seca in 2008, while more recently Rossi was responsible for the Australian's only DNF of 2011 after sliding into him at Jerez.
Rossi said he places Stoner on the same level as his great rivals Max Biaggi and Sete Gibernau, and was consequently thrilled to have beaten him.
"Having managed to beat him makes me very happy, almost more than for the podium - I think this is already our sixth scrap," Rossi said.
"I place him on the same level as my historic rivals Biaggi and Gibernau. Last year at Jerez I crashed into him, while this time I was more careful."
Despite his satisfaction over the Le Mans result, Rossi warned that Ducati was still a long way from winning in the dry.
"A second place is not like a victory," he insisted. "We want to learn how to go as quick in the dry as in the wet. When you hope it rains, that means you're in the shit.
"We haven't yet understood why, but the Ducati goes a lot better in the wet. It was most of all a bike success."