Sorensen was part of a small group of seven riders that finished several minutes ahead of the main pack after foraging ahead unchallenged during the 211.5-kilometer (131.4-mile) trek from Tonnerre to Vittel, which featured six small hills.
The Danish veteran, after years as a support rider in Bjarne Riis' team, finally earned his first career stage win on the three-week race, and finished 48 seconds ahead of Lefevre.
"I'm 34 years old now and it's a big thing for me to perform at this level at this age," Sorensen said. "I started bike racing when I was 19 and I always hoped that I could maybe go on for many years and I think it shows today that it is possible."
The chasing pack, including Nocentini, seven-time champion Lance Armstrong and Alberto Contador, finished nearly six minutes behind. Contador remained in second place overall, with Armstrong in third.
"We let the breakaway go after four minutes," Nocentini said. "It's a tough stage tomorrow but I'm already really happy and I will do my best to keep the yellow jersey tomorrow."
Seven riders managed to get away after about 65 kilometers (40.3 miles), including Egoi Martinez, Franco Pellizotti, Remi Pauriol, Sylvain Calzati and Markus Fothen.
The main pack sat up and let the breakaway go, with Mark Cavendish's Team Columbia-Highroad teammates not chasing. Cavendish has been the best sprinter at this year's Tour with four stage wins, including on Tuesday and Wednesday.
Calzati and Sorensen worked together to build a lead of 15 seconds with about 10 kilometers (6.2 miles) remaining, but Sorensen attacked with about 2 kilometers (1.25 miles) to go and the others could not follow.
Armstrong looked to be in trouble after about 60 kilometers (37 miles) when he had to pull over to let his Astana team repair a puncture in his back wheel. However, after just a few moments, four of Armstrong's teammates helped him catch up with the main pack again.
"Up and down all day long and was aggressive from the start," Armstrong, who didn't speak to reporters after the stage, said on his Twitter feed. "Took 80 kms (kilometers) for the break to go. Ouch. Also pretty warm."
The Texan said before the stage that his main objective was to avoid any major incidents. Wednesday's stage was marred by several crashes and 19 riders were slightly injured.
"Yesterday, there was no way to avoid that crash. If you were just behind it, you were going down," Armstrong said. "So that is something which keeps you up at night. You have to constantly pay attention. I try to give myself a bit of space from people in front of me so I have a bit of time to brake."
Also Thursday, the International Cycling Union said in a statement that an earpiece ban set for Friday's 13th stage from Vittel to Colmar has been overturned, and riders will be able to race with electronic radio equipment as normal.
