Andy Schleck, who currently leads the Yellow Jersey standings, finished fourth 1:08 minutes behind Riblon, in a group that also included his closest rival, defending champion Alberto Contador of Spain.
Race for Yellow
Schleck and Contador had stuck together throughout the 184.5km stage from Revel, the first stage of the this year's tour in the Pyrenees mountains.
Schleck said he had not dared overtake Contador for fear that the Spaniard would launch a late attack and go past him.
"I feel really good, and if he wants to get me tomorrow, he has to be really good," he said.
"I don't know how [Contador] feels right now. This is just a guess, but I guess he's not happy," Schleck said. "He didn't lose any time but he didn't gain any either."
Schleck leads the race by 31 seconds from Contador, with Sanchez now 2:31 back and Menchov in fourth at 2:44.
But the Saxo Bank rider needs to maintain the gap over Contador as the Spaniard is likely to dominate Satruday's final time trial stage.
"I'm in a good position. [The 31 seconds] is a difference that I can erase in the final time trial. It is a face-off," Contador said.
Monday's 15th stage is the second in the Pyrenees and takes the riders 187.5km from Pamiers to Bagneres-de-Luchon, over the major climb of Port de Bales before descending to finish on the flat.
Meanwhile, seven-time champion Lance Armstrong dismissed reported claims by fellow American champion Greg LeMond that he had sought to pay someone to allege LeMond used EPO, a banned performance enhancer.
|Armstrong has struggled to keep up with the pace on his final attempt at the Tour [Reuters]
"That's absolutely nonsense. $300,000?'' Armstrong said, when asked by The Associated Press news agency about the allegations.
"Come on. I know [about the claims]. But he says a lot."
According to media reports, LeMond has been served with a grand jury subpoena as part of a federal investigation of possible fraud and doping charges against Armstrong and his associates.
The two Americans have a long history of mutual antagonism as LeMond has frequently questioned his compatriot's record-setting performances.
Armstrong has had a difficult final tour, finishing Sunday's stage in 70th place, 15 minutes 14 seconds behind Riblon. He is 38th in the overall standings, 39:44 off the pace.