The breakaway group finished one minute, 55 seconds ahead of the peleton with the overall leaders --- including eighth-place Lance Armstrong --- remaining in the same spots they had occupied at the start of the day.
A major shakeup in the standings is expected Monday, however, when the riders take part in a 52-kilometer individual time trial. Armstrong, seeking his fourth Tour de France championship, could be leading by the end of Monday's ride.
Kroon, riding for the Rabobank team, led a Dutch sweep of the top three places as Servais Knaven finished second and Erik Dekker third. The Dutch riders worked together over the final kilometer to spoil a bid by the three French riders in the breakaway to capture a win on Bastille Day.
Frenchman Franck Renier, who among those in the break was the best-placed rider in the overall standings, finished fourth, followed by countrymen Sebastien Hinault and Stephane Auge. The other member of the break was Raivis Belohvosciks of Latvia.
The group of seven opened as much as a five-minute advantage over the peleton during a 217-kilometer ride from Saint Martin de Landelles to Plouay that took the tour through the heart of Brittany.
Renier was the biggest threat to the overall leaders, having started the day 4:39 behind. And once the peleton reduced the deficit to about three minutes, the chasers lost interest and the frontrunners were allowed to finish well in front.
Igor Gonzalez Galdeano of Spain remained the overall leader, four seconds in front of countryman and ONCE teammate Joseba Beloki. Armstrong, whose usual dominance in time trials and in the mountains make him the runaway favorite to win another title, will go into Monday's ride 34 seconds behind.
As the overall leader, Galdeano will be the last to start the individual time trial, which will take the riders from Lanester to Lorient.
After the time trial, the riders will have a day off. The first major mountain stage will come next Thursday and after that climb into the Pyrenees, Armstrong is expected to have put his stamp on this tour. The race ends July 28 in Paris.