MEGEVE, FRANCE >> Take it from cycling great Eddy Merckx: nobody can beat Chris Froome in this Tour de France.

Riding with the poise and purpose of the Tour's undisputed leader, Froome won a mountain time trial in Stage 18 on Thursday and opened up a seemingly insurmountable lead of nearly four minutes over his closest challenger, Dutch rider Bauke Mollema.

Only two Alpine stages remain before Sunday's mostly ceremonial finish on the Champs-Elysees in Paris.

"He deserves his win. He's the strongest," said Merckx, a five-time Tour winner. "I can't see what could prevent him from keeping this yellow jersey until Paris. His opponents just stay on his teammates' wheels. Barring an incident, nobody can beat him in this Tour."

Riding in a yellow bodysuit and yellow aerodynamic helmet, Froome pumped his right fist after clocking slightly more than half an hour over the 17-kilometer (10.5-mile) route from Sallanches to the Megeve ski resort — which featured majestic views of Mont Blanc.

Froome finished 21 seconds ahead of Dutch rider Tom Dumoulin to take his second stage win of this year's Tour.

"That's a huge compliment coming from Eddy," Froome said. "Obviously we feel like we're in a bit of a bubble in the race here. But to have somebody like that give a compliment like that is a great honor."

Froome increased his overall lead to 3 minutes, 52 seconds over Mollema, with Adam Yates of Britain third, 4:16 behind.


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Two-time runner-up Nairo Quintana stayed fourth but now trails by 4:37 after another difficult day for the Colombian.

"The main thing for me now is staying safe," Froome acknowledged. "Obviously I've got a fantastic advantage now. So now it's about looking after that advantage and not taking any risks.

"It's not over until we cross that final finish line, but today is a huge boost of confidence," Froome added. "I think over these next couple of days we're going to see more of a race for podium spots."

Froome stood only fifth at the first checkpoint, the top of the Cote de Domancy climb, but the British rider clearly saved energy for the second half of the stage, surging in front over the final kilometers.

"Froome just showed he is the strongest," said Dumoulin, who rode 90 minutes before the race leader.

Spanish Vuelta champion Fabio Aru of Italy finished third in the stage, 33 seconds behind.

It was the Tour's first mountain time trial since the 2004 race against the clock up l'Alpe d'Huez. Besides the flat opening four kilometers (2.5 miles) and a short descent at the finish, it was entirely uphill.

Froome's other stage win this year came with an audacious downhill attack in Stage 8 in the Pyrenees. The Kenyan-born rider with Team Sky also won a time trial in the 2013 Tour, when he took his first overall victory.

Having also won the Tour last year, Froome is on course for his third title in four years.

Considering that most of the route was uphill, many riders used road bikes fitted with bars to lay their arms on for a more aerodynamic position.

Froome was one of the few riders to use a full time trial setup with an aerodynamic rear disc wheel instead of traditional spokes.

"I think that was a big part of today's stage — selecting the right equipment," Froome said. "The other aspect of today was pacing. It was important not to go too fast too early."

Fans lined the major climb of the route, the Cote de Domancy, getting up close to the riders to shout encouragement — with glaciers and snowcapped mountains in the distance.

Stage 19 on Friday follows a 146-kilometer (91-mile) route over four ascents from Albertville to Saint-Gervais Mont Blanc. The penultimate leg on Saturday concludes with a tricky descent to Morzine after four more climbs through the Alps.

"Tomorrow is a very tricky stage with a lot of tricky descents. There's talk about thunderstorms during the race. It's definitely going to have to be a stage where we stay right on our game," Froome said.

"We can't relax and switch off now," Froome added. "We've got to see this through right to the end."

AP Sports Writer Samuel Petrequin contributed to this report.