VITTEL, France — Lance Armstrong remained in third place at the Tour de France on Thursday, scrambling back to the main pack following a punctured tire with about 37 miles left.

Teammate and rival Alberto Contador of Spain stayed in second place and Rinaldo Nocentini of Italy kept the yellow jersey on a day Nicki Sorensen of Denmark won the 12th stage.

"Up and down all day long and was aggressive from the start," Armstrong said on his Twitter feed.

Sorensen broke away and finished 48 seconds ahead of Laurent Lefevre of France. The 34-year-old Dane spent years as a support rider for Bjarne Riis and this was the first time he won a Tour stage.

"It's a big thing for me to perform at this level at this age," he 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."

Armstrong, the seven-time champion, rejoined the main pack after his mishap during the 131-mile ride from Tonnerre to Vittel. He pulled over to the side of the road while his team repaired a punctured back wheel. After a few moments, four teammates helped him catch up.

Armstrong is taking a cautious approach until the three-week race reaches the Alps on Sunday. He said the flat stages were nerve-racking.

"It is stressful with the crashes, on a stage like this where you have nothing to gain and then you lose everything because of a crash or a split in the group," the 37-year-old Texan said before the start. "You have to pay attention and try to avoid a crash."

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."

Riders also learned that an earpiece ban scheduled for Friday's stage was overturned, allowing them to communicate by radio with team cars as usual. The ban was in place Tuesday and another was set for the 13th stage before the International Cycling Union reversed itself.

Many riders and team directors called the ban dangerous. Organizers hoped the experiment would inject drama into the race by having riders fend for themselves.

Sorensen was part of a lead group arriving several minutes in front of the main pack. The group was unchallenged and the chasing pack — including Nocentini, Contador and Armstrong — was nearly six minutes back.

"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."

Seven riders managed to get away after about 40 miles, including Egoi Martinez, Franco Pellizotti, Remi Pauriol, Sylvain Calzati and Markus Fothen.

The main pack let the breakaway go, with Mark Cavendish's Team Columbia-Highroad teammates not chasing. Cavendish has been the best sprinter on the Tour with four stage wins, including Tuesday and Wednesday.

Calzati and Sorensen worked together to build a lead of 15 seconds with about six miles remaining, but Sorensen attacked with just more than a mile to go and the others could not follow.

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AP Sports Writer Samuel Petrequin contributed to this report.