Denmark's Jonas Vingegaard, wearing the overall leader's yellow jersey, and Slovenia's Tadej Pogacar, wearing the best young rider's white jersey, pump fists. Photo / AP.

Jonas Vingegaard thundered through the last serious test of the Tour de France to increase his overall lead on Saturday and all but guarantee winning cycling's biggest race.

After three weeks of exhausting racing, the Jumbo-Visma leader dug deep in his reserves to deliver yet another impressive performance in a long time trial in southern France.

"It means everything, it's really incredible," Vingegaard said. "It's the biggest thing within cycling and we did it."

Vingegaard, who is not a pure specialist of the race against the clock, could have played it safe given his more than three-minute lead at the start.

He, instead, took all the risks on the technical course and had a scare close to the finish when he misjudged a curve and had to brake hard to avoid a crash.

Vingegaard then slowed down dramatically as he approached the finish line. He finished the 20th stage in second place 19 seconds behind winner Wout van Aert, his key teammate.

Vingegaard and Van Aert hugged each other warmly at the finish and the Danish rider was emotional after he was greeted by his wife and daughter after the stage.

"Having my two girls on the finish line means even more to me," said Vingegaard, who improved on last year's runner-up finish.

"Since last year, I always believed I could do it and now it's happened. It's really incredible. It's both a relief and I'm just so happy and proud."

Van Aert, a versatile competitor with multiple titles and wins across the sport's most prestigious events, has been crucial in pacing Vingegaard through the mountain stages.

His third stage win this month was his ninth overall.Van Aert, who also claimed the best sprinter's green jersey, has proved he can win on all surfaces and could be a leader in his own right in any given team.

He has so far deflected talk of mounting a challenge for the yellow jersey in the future."This has been the question over the last few days, I think," Van Aert said.

"I have answered a thousand times. Right now, it's just an incredible feeling to win this Tour with the team and to win three stages and the green jersey. For the moment, I don't want to talk about the future."

Van Aert crossed the finish line with a blistering average speed of 50.9 kph. The 41.7-kilometer stage from Lacapelle-Marival to Rocamadour was the longest individual time trial since 2014.

With the final day of the race on Sunday usually uneventful until the last sprint on the Champs-Elysees, Vingegaard will become the first rider from Denmark to win the Tour since 1996, barring a crash or a last-minute incident.

The time trial marked the final hurdle of an epic race that has featured a thrilling duel between Vingegaard and two-time defending champion Tadej Pogacar.

Vingegaard built his success in the mountains. He first took the yellow jersey from Pogacar in the Alps with a memorable ride up the Col du Granon, and followed up this week with an impressive display of strength in the last Pyrenean stage to the resort of Hautacam.

Given Vingegaard's healthy time advantage, it was unlikely Pogacar would be able to challenge the Danish rider's supremacy in the time trial. Pogacar took third place, 27 seconds behind Van Aert.

"The battle between me and Jonas for the yellow jersey has been very special," Pogacar said. "We have some very interesting next two or three years ahead of us. Jonas has stepped up his game this year."

Vingegaard will carry a lead of 3 minutes, 34 seconds over Pogacar into the final day, a 116-kilometer ride to Paris. Geraint Thomas, the 2018 Tour champion, lagged more than eight minutes off the pace in third place.