JOIGNY, France -- Fabian Cancellara says he knows his days in the Tour de France's yellow jersey are numbered as the race heads toward the Alps.
The Swiss time-trial ace kept the prized race leader's shirt after yesterday's fourth stage, a mostly flat 119.9-mile ride from Villers-Cotterets to Joigny won by Thor Hushovd of Norway.
No rider has threatened Cancellara's lead since he won Saturday's prologue and extended his margin with a daring win in stage three Tuesday, but others are stronger climbers.
"For me, when I get into the mountains, it's sure that it's finished," Cancellara said of his run as the leader.
Hushovd, who won the green jersey awarded to the Tour's best sprinter in 2005, overcame stomach pain to earn his fifth Tour stage win with a final sprint, finishing ahead of South Africa's Robert Hunter in second and Oscar Freire of Spain in third.
"Everything took place superbly well," said Hushovd, who took first in 4 hours, 37 minutes, 47 seconds. "I'm too happy.
"I was sure my form wasn't too bad."
The Norwegian climbed from ninth to second place and gained bonus points for the victory that put him 29 seconds back of Cancellara. Andreas Kloeden of Germany, who was runner-up to Lance Armstrong in 2004, is third, 33 seconds behind.
Riders break out of the flats today with a 113.4-mile trek from the Burgundy town of Chablis to Autun featuring eight medium-grade climbs.
"Someone's really going to have some guts to go for it tomorrow," said Cancellara's CSC teammate Christian Vandevelde of the United States. "People are going to be biding their time thinking about [the Alps]."
In the Alpine stages of the three-week race, overall favorites could try to make their move and chisel out precious minutes on their rivals. Few can be ruled out yet: 160 riders are within two minutes of Cancellara.
Kazakhstan's Alexandre Vinokourov is widely seen as the top contender, though Kloeden, U.S. rider Levi Leipheimer, Australia's Cadel Evans, Russian Denis Menchov and Spaniards Alejandro Valverde and Oscar Pereiro are all strong possibilities.
Two riders dropped out after crashing early in yesterday's stage. Xavier Zandio of Spain broke his right collarbone and France's Remy di Gregorio broke his right elbow.
A total of four riders have pulled out, leaving 185 riders left.
The Tour, in its 94th edition, is taking place as cycling has suffered huge blows over the past year because of doping allegations involving some of the sport's biggest names.
Would-be title contenders such as Italy's Ivan Basso and American Tyler Hamilton have been forced to sit out over doping probes, and few experts believe that the peloton -- or rider pack -- is fully clean.
The 2006 champion, Floyd Landis, is also out, and awaiting an arbitration panel's verdict whether he can keep the title after testing positive for synthetic testosterone in Stage 17 last year.
The International Cycling Union, or UCI, has publicly sought to crack down.
All Tour racers signed a new UCI anti-doping charter in time for Saturday's start, saying they are not involved in doping and promising to submit DNA samples to authorities for a vast probe called Operation Puerto, which erupted in May 2006. Cyclists also had to agree to pay a year's salary on top of a two-year ban if caught doping.
The UCI this week said it wants team managers and staff to sign a similar pledge by Aug. 1 -- three days after the Tour ends.
Stage: The final sprint of the week covered a 119.9-mile route from Villers-Cotterets to Joigny.
Winner: Thor Hushovd of Norway. Robert Hunter of South Africa was second, Oscar Freire of Spain third.
Yellow jersey: Fabian Cancellara of Team CSC, leads Hushovd by 29 seconds and Andreas Kloeden by 33.
Quote of the day: "We said at the start of the stage that if we win, it's a Chablis. And if we lose it's a Chablis anyway," Hushovd's teammate Christophe Le Mevel on the team's plan to take in some of the region's fine wines.
Next stage: The fifth stage today is a medium mountain stage taking riders on a 113.4-mile trek from Chablis to Autun.