Chris Froome on the Ax3 Domaines stage....

After my long ride, and a visit to the pub, I settled down to catch up on stage 8 - I'd seen the first part live whilst visiting my Mum, and the race was developing into a classic cat and mouse battle in the mountains - I hadn't anticipated quite how it would turn out though!

This was not so much a statement as a massacre. It took just five kilometres for Chris Froome to leave his rivals stretched so far down the road to Ax 3 Domaines they resembled coloured dots – and to open up a gap in this year's Tour de France that may prove permanent.

Up close, you could see the terrible suffering that Froome's savage tempo had wrought. Alberto Contador's face was contorted, as if undergoing a Chinese burn, as he crossed the line 1min 45sec back. Cadel Evans, the winner of the Tour as recently as 2011, looked all of his 36 years as he struggled in 4:13 behind. For others the pain – and the time deficit – were even worse.

Meanwhile Froome could hardly stop smiling. A plan to put Froome into the yellow jersey in the Tour's first stage in the mountains had worked to perfection. And beyond their wildest dreams.

"This is incredible," Froome said. "We have worked for months to be in this position. Once I pulled clear of the other guys with 4-5km to go, I knew I had to go into almost time-trial mode to take the biggest advantage possible. I definitely wasn't holding anything back. This is the Tour de France. Every second counts. I wasn't trying to save myself."

On this day last year, Froome won a similar stage in the mountains – and watched as Bradley Wiggins became the fifth British rider to wear the yellow jersey. Now Froome has become the sixth, joining Wiggins, Tom Simpson, Chris Boardman, Sean Yates and David Millar.

Everyone remembers last year's Tour as a procession for Team Sky, and in the end it was, but at this point in the race Wiggins led Cadel Evans by only 10 seconds. Froome, however, is already 51 seconds clear of his team-mate Porte and 1m 25 ahead of Alejandro Valverde, with Contador a further 26 seconds behind. It is a big lead. It could be a winning one. Naturally there will be caveats and cautions – there are still another 13 stages and 2,000km worth of racing to go. But the race is now Froome's to lose. He will be expecting to emulate Wiggins in keeping the yellow jersey from now until Paris.

On the eve of the first mountain stage Sky had predicted cagey sparring. Instead they delivered a knockout blow. Initially, while the riders' skin burned in the 33-degree heat, the race simmered for the first 140km. When four riders made a break within the first kilometre of stage eight they found themselves pushing at an open door; the main contenders for general classification bided their time and conserved their energy for what lay ahead. They knew that the 15km climb up the 2,001m Col de Pailhères, the highest in this year's Tour, would act as a natural brake.

It did. Soon the riders were stretched along the road like a piece of string. As the leading group went through the pretty mountain village of Mijanès there was a sign informing them they were 1,139m above sea level. That meant there was still nearly 900 painful metres to go.

At that point the Frenchman Christophe Riblon, who won the stage finish in Ax 3 Domaines in 2010 and was part of the initial breakaway, decided to attack, vaguely hoping for a repeat performance. There were also guerilla attacks from Robert Gesink and Thomas Voeckler that soon fizzled out.

However towards the middle of the climb up the Col de Pailhères Movistar's 22-year-old Colombian, Nairo Quintana, launched a break that had legs. When he was a child Quintana used to ride up a 16km mountain with an 8% ascent to school. The road up the Col de Pailhères was almost identical. No wonder he looked at home. Quintana had a lead of more than a minute going over the summit but that had halved by the descent as Team Sky's group of riders – Kennaugh, Froome and Porte – worked patiently. Behind them, Contador and his Saxo-Tinkoff team watched every move. By now the yellow jersey, Daryl Impey, had slipped back, unable to handle the pace.

With 7km to the summit of the day's final climb to Ax 3 Domaines, Porte steadily sweated up front. Soon Contador was cracking, while everyone else was grimly hanging on. Then, with just over 5km to go, Froome kicked for glory, jumping past Porte and then Quintana and racing alone into the lead.

At the 5km flag he looked around but his rivals were scattered. Now it was time to push on. His teeth were gritted now, the head rocking. As the crowds parted for him and his mouth opened to gasp more of the thin mountain air you could almost detect a smile.

"I was a little surprised at what happened," Froome said . "I expected attacks from more of the GC contenders but I know Richie and I are in really good condition and have been training for months to be in this position."

Afterwards he smiled as he received the yellow jersey before kissing two brunettes on the podium and punching the sky with flowers and his winner's trophy. He better get used to the experience. There will be much more of this in the coming days.