The smile on Alberto Contador’s face as he sprinted towards the finish line at the Andorran ski station of Arcalís on Friday said it all. The 26-year-old Spaniard was not racing towards the yellow jersey, or even a stage win, but by attacking in the closing kilometres of the Tour de France’s seventh stage he regained the upper hand in the astonishing power struggle with Lance Armstrong that threatens to split the Astana team in two.

Contador and Armstrong entered this race just over a week ago with equal billing. Well, equal billing in that they each felt they had the right to be considered the true leader of the Astana team.

Armstrong, the seven-time Tour champion, has not ridden the event since his retirement in 2005, but has vast experience and the support of the team’s manager, Johan Bruyneel, in his favour. Contador, the 2007 Tour winner, is the only current rider to have claimed all three of the sport’s grand tours, the others being the Giro d’Italia and the Vuelta a España. He is the finest mountain climber of this generation.

Since the race began in Monaco, the pendulum of power in the Astana team has swung this way, then that, and each time the thin veneer of tolerance the two protagonists have for each other cracks a little more. In the opening day’s individual time trial, Armstrong was only the fourth best rider in the Astana team, finishing 22 seconds slower than Contador and 40 seconds behind the stage winner Fabian Cancellara, a Swiss rider with the Saxo Bank squad. Armstrong’s too old, they said, and that result showed it.

After four years on the couch, few thought the 37-year-old American could match the Spaniard, whose climbing style mimics that of Armstrong in his pomp. A broken collarbone in a small Spanish race in the spring threatened to derail Armstrong, but he recovered quickly enough to bank his appearance fee at the Giro d’Italia, where he was 12th overall. Good, but not the level of performance Armstrong was accustomed to. The Tour, most pundits agreed, would be even tougher.

This cycling comeback was billed in part as a global campaign to raise awareness for cancer, its sufferers and survivors. Strangely, Armstrong has not spoken much, if at all, about the illness that struck him in 1996, not even at the official pre-race presentation in Monaco. A week into the race, there is no doubting his real motivation here. He is as wrapped up in the minutiae of the race and as obsessed with his standing in the sport as he ever was.

Armstrong is dogged and fiercely motivated by every slight, both real and imagined, but anger and determination will take him only so far.

Before the stage to Arcalís, many were anticipating an Armstrong attack, perhaps midway up the climb, like he did in the old days. The Texan’s modus operandi was always to attack hard and decisively on the Tour’s first mountain-top finish, then use his team to defend the lead. That he didn’t suggests only one thing. He couldn’t do it.

According to Armstrong, Contador’s attack in the final two kilometres of the climb defied team orders. “It wasn’t really to the plan, but I didn’t expect him to go by the plan. It’s no surprise,” he said, his tone scarcely concealing his anger. “When you’ve got a guy away, like I said all along, my obligation is to the team.” It was odd to hear Armstrong talk of his obligation to the team, only four days after helping to stitch up Contador on the road to La Grand Motte.

On Monday’s third stage the peloton split in the crosswinds about 30 kilometres from the finish. The Columbia team, who had done all of the work to bring back a breakaway and set up victory for their sprinter Mark Cavendish in Brignoles the previous day, were frustrated at the lack of co-operation in the peloton, and decided to make them pay by increasing the pace.

A subtle change of direction meant the wind was cutting across the bunch, forcing them to fan out across the width of the road and making a split inevitable. It was here Columbia upped the tempo and a gap opened. Twenty-seven riders went clear. Crucially, Armstrong made it with a couple of team-mates, while Contador missed out.

With 15 kilometres to go, Armstrong chose to exploit the break to his advantage, instructing his two team-mates, Yaroslav Popovych of Ukraine, and Haimar Zubeldia, another Spaniard, to assist Columbia. At the finish, Armstrong had gained 41 seconds, leapfrogging Contador by 19 seconds. The time gap was not important, the pecking order was.