Armstrong, going for a seventh straight Tour victory, crossed the finish in 45th place in a pack of riders that clocked the same time as McEwen — 3 hours, 46 minutes — for the 113.7-mile ride from Chambord (search) to Montargis. He has the yellow jersey for the 68th time.
McEwen, of Davitamon-Lotto, sped ahead of Belgian Tom Boonen in a final sprint to collect his sixth Tour stage win and his first this year. Boonen has won two stages this year, both sprint finishes.
The nervous pack of riders battled wind, intermittent rain and slick roads, and there were several crashes. CSC leader Ivan Basso, seen as a potential contender for a Tour victory, was a crash victim.
Armstrong took the yellow jersey Tuesday from fellow American David Zabriskie, a Team CSC rider who fell in a dramatic crash in the final moments of the stage.
The six-time Tour winner started the day opting not to wear the leader's yellow jersey, citing "respect" for Zabriskie. Armstrong set off in his Discovery Channel uniform in the pre-race ride, but race officials stopped everybody before the starting line and asked Armstrong to wear it.
"There was no problem, just a little confusion in the beginning, having not started in the jersey," Armstrong said. "I didn't feel that it was right to start in the jersey."
Tour director Jean-Marie Leblanc got strict about the rule book, which states that the overall race leader "must wear" the yellow jersey.
"There was no negotiation," Armstrong said. "Jean-Marie said: 'You don't start in the jersey, and you don't start tomorrow."'
Before the stage, Armstrong wanted to follow an unofficial tradition by not donning the jersey.
"In light of the tradition of the last 30 or 40 years, no one really takes it if there is a crash" involving the race leader, he said. "We decided to leave it empty today."