(CNN) Defending champion Geraint Thomas made up nearly half a minute on leader Julian Alaphilippe in a gripping 15th stage of the Tour de France in the Pyrenees on Sunday.
A former winner of the event said the day could be significant in deciding the race's outcome.
Thomas shaved off 27 seconds, pulling away from the less experienced Alaphilippe with around 1.5 kilometers (0.93 miles) remaining in the 185-kilometer (115-mile) section between Limoux to Foix Prat d'Albis. He now trails Alaphilippe by one minute, 35 seconds.
"Geraint will now start to think he can win this race again," said 2012 champion Bradley Wiggins, analyzing the race for British Eurosport.
Wiggins said Alaphilippe's failure to pace himself cost him in the stage and could hurt his overall chances as he bids to become the first Frenchman to win cycling's most famous race since Bernard Hinault in 1985.
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"That's what will lose him the Tour de France, that inability to gauge his effort over the three weeks," said Wiggins. "He's full-on all the time. He's a puncher, he rides on morale, he rides on the crowd supporting him.
Wiggins suggested Alaphilippe should "have just stayed with Geraint the whole way up the climb," adding that the Welsh cyclist "is actually the only man he should keep his eye on at the moment.
"If he wins this Tour, he's going to have to get a lot smarter."
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Alaphilippe said he was simply happy to keep the leader's yellow jersey for another day.
"We knew it would be a hard day," he was quoted as saying on the Tour's website. "I paid for my efforts in the finale. I expected to lose a bit of time today.
"I'm delighted that I'm still in the yellow jersey. I gave my best to fight and retain the lead. The dream goes on. I was never a favorite and the hardest is yet to come."
Thomas said his legs "are responding a little bit better," but he admitted he's still thinking about last year's race, which produced a fourth straight winner from the UK.
In Saturday's grueling 14th stage between Tarbes and Tourmalet, Thomas lost 30 seconds on Alaphilippe.
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"It's just such a mental game," the Welshman told reporters. "Everyone is good. Everyone is tired, and you sort of just need to block that out.
"It's just easy to think about last year and think of all the good times ... but I was suffering at times then as well, so I just need to bite the bullet and dig in."
Perhaps the biggest winner of the last two stages was another Frenchman, Thibaut Pinot.
He shone Saturday to close within three minutes, 12 seconds of Alaphilippe. After breaking away to finish second Sunday behind Britain's Simon Yates, Pinot now sits fourth, only one minute, 50 seconds behind the leader.
Yates finished ahead of Pinot by 33 seconds on Sunday. It was his second victory in less than a week after triumphing in stage 12.
The riders have a much-needed day off Monday before a respite from the mountains: A 177-kilometer (110-mile) stretch that starts and ends in Nimes.