Overall leader Lance Armstrong was content to stay in the pack since none of his major rivals tried to join Saturday's break and he maintained a comfortable advantage in search of his fourth consecutive championship.
It was the second stage win of Millar's career, but the first on a road course as he covered the 171 kilometers from Lavelanet to Beziers in four hours, eight minutes, 18 seconds. He outsprinted Spain's David Etxebarria to the line at the end of a relatively flat stage that came after two mountain stages during which Armstrong took charge of the tour.
The 11-rider breakaway opened as much as an 11-minute lead on the peloton and included in the break was Laurent Jalabert of France. It was the third straight day Jalabert has tried to get away from the field as he rides in his final Tour de France.
He wound up at the end of the breakaway group Saturday, in 11th place and 1:10 behind Millar. The peloton finished 9:56 back of the stage winner. But none of those in the break were close to the overall lead when the stage began, so Armstrong and his United States Postal Service teammates were content to let the small group open a big gap.
Armstrong, who won both the Thursday and Friday rides through the Pyrenees, leads Spain's Joseba Beloki by 2:28. Igor Gonzalez Galdeano of Spain is 3:19 back, followed by Raimondas Rumsas of Lithuania (5:15) and Colombia's Santiago Botero (5:44).
Jalabert's efforts Saturday moved him into ninth place overall.
Another mountain stage will be ridden Sunday with a closing climb that could give Armstrong another chance for a stage win. He has won three stages this year, including the short individual time trial that began the tour.