Richie Porte banished memories of a bad day in the Pyrenees by dropping some of the best climbers in the Tour de France on Sunday to launch his team leader Chris Froome to victory on Mont Ventoux.

The Tasmanian's impressive ride came on a day when former winner Cadel Evans (BMC) lost big time and any realistic chance of a top-10 finish.

Sky's Porte went to the front with 10km to go on Sunday and lifted the pace until only Froome and former winner Alberto Contador (Saxo-Tinkoff) remained on his wheel.

The 28-year-old's effort dispatched most of the general classification (GC) contenders, including Bauke Mollema and Laurens ten Dam (Belkin), leaving only Colombian Nairo Quintana (Movistar) up ahead.

Froome came out of Porte's slipstream with just over 7km remaining and quickly distanced Contador before catching and passing Quintana.

The yellow jersey holder was thrilled with Porte's work.

"When Richie took over, he really upped the pace and, in the process, got rid of the big GC guys on our wheels," Froome said after the finish.

Porte's form has been mixed. He smashed the race to pieces on the first day in the Pyrenees but was dropped early last Sunday on the road to Bagneres-de-Bigorre.

He came fourth in the individual time trial on Wednesday but was then distanced on the road to Saint-Amand-Montrond.

Porte's blistering pace on Sunday was too much for Contador's Australian teammate Michael Rogers who fell back with 8km left to race.

But the Canberran is now Australia's top rider on GC in 12th place after Evans' "horrible" ride on Mount Ventoux in which he tumbled to 16th overall.

"What can I say?" Evans said after the stage.

"Nowhere near where I wanted to be. I had a lot of difficulties."

The 2011 winner said he was tired at the start of the Tour's longest stage and exhausted before the peloton reached the foot of the legendary 21km Mont Ventoux.

"As the climb went on, (I felt) worse and worse - and when you are popped out of the group, it doesn't do a great deal for your motivation."

Evans finished the 15th stage 8:46 behind Froome who ended up winning by 29 seconds over Quintana. The Sky leader put 1:23 or more on his other rivals.

Froome, who needed "five or 10 minutes on the oxygen" mask after the stage, leads Mollema by 4:14 and Contador by 4:25.

"It wasn't really about sending (Contador) a message but I'm obviously going to take as much time as I can," Froome said.

"I'm really happy to have this advantage now."

Following Monday's rest day, there is a medium mountain stage on Tuesday, then a 32km time trial and three straight days of tough climbing in the Alps.