Keeping a lid on Hamilton and Rosberg

A brief embrace, then congratulations: at first, it seemed Nico Rosberg's reaction to Lewis Hamilton's third world title would be tiresomely magnanimous. But this bonhomie in the weighing room immediately after the US Grand Prix was short-lived. Having managed the minimum of manners, Rosberg's mood soured.

After a bear hug with Mercedes technical whizz Paddy Lowe, Hamilton went to gather up his winner's cap, ready for the podium ceremony. This cap carries a golden "1st" emblazoned on the side. Next, Hamilton picked up the "2nd" cap and tossed it into Rosberg's lap, as the German - now looking sullen and introspective - slumped in a nearby armchair. Rosberg glanced at the headware then hurled it straight back, accurately too, almost dropping it back into Hamilton's hands.

Rosberg later described this as "just one of our games," but it didn't seem so playful.

Matters scarcely improved on the podium or in the press conference immediately thereafter. As four-time champ Sebastian Vettel, who came in third in Austin, doused the chasing Hamilton in bubbly in front of the Texan fans, Rosberg stood arms folded on the platform, looking ready for a rather stiffer drink, consumed in privacy.

Once on the microphone, Rosberg came closest to vocalizing his frustrations at the very end, when given the chance to offer a statement in German. Hamilton's first-corner overtake, pushing Rosberg off the track in the damp to claim the lead, "went a step too far," Rosberg said.

For Hamilton, the situation looked different: "I don't feel like it was aggressive. At the end of the day, I was on the inside so it was my line."

It's not the nudge that pushed Nico over the edge

Hamilton's first-corner maneuver did push the boundaries of collegial driving; a move that would be cruel but kosher against any car on the grid, except perhaps against your teammate. Still, Rosberg probably had other, much more troubling issues on his mind than Hamilton's aggressive driving style - which has been the paddock's worst-kept secret since 2007 anyway.

Rosberg turned 30 this summer. He's married, and had his first child this season. He's barely six months younger than Hamilton, while Vettel's two years younger than the Mercedes duo. If Rosberg intends to join his contemporaries as more than just a race-winner, time is running short. The last man to seal a world title on US soil - as some paddock historian surely reminded Rosberg this weekend - was Keke Rosberg back in 1982. Nico's spent his life looking to emulate his Finnish father; Sunday's race could have raised doubts.

For three seasons, Rosberg has kept teammate Hamilton honest. He's solid in developing the car, an engineers' favorite known for excellent technical feedback, and he's proven to be a consistent and quick qualifier, able to fight Hamilton for pole position. However, Rosberg has won just two of the last nine races he started on pole position. From the front of the grid, Hamilton has seven wins from 10 this season. Austin's 2014 Grand Prix was the same story: Rosberg on pole, Hamilton passes during the race to claim victory.

When push comes to shove on Sundays, it tends to be Rosberg who yields. He even recovered at Austin after Hamilton's first-lap bump, retaking the lead and holding all the aces when the final safety car was deployed. It was looking like one of the German's best races of the season. Soon after the restart, though, Rosberg spun his wheels, ran wide, and allowed Hamilton through to title No. 3. It was this mistake, not Hamilton's first-lap pass, which ultimately cost Rosberg the race.

An opportunity for Vettel?

The danger, at least for team Mercedes, is that Rosberg reappraises his own policies when wheel-to-wheel with Hamilton. After his least competitive season in three driving alongside Hamilton, Rosberg cannot be content with the status quo. Drivers with their backs to the wall tend to be tougher to pass than contented teammates, and Hamilton won't stop looking to get by. If Rosberg stops driving cooperatively, the pair could collide again.

There are plenty of points - and points mean prize money - still to win in the last three races of the season. But more than that, Mercedes have both drivers contracted for another season, with no real motivation or scope to change the line-up.

"It's never easy for things to cool down. It wasn't easy the first time around, but we have some experience," the team's motorsport boss, Toto Wolff, said after the race. "But it is also a crucial moment now to make sure this race and incident don't release consequences within the team and split the two sides of the garage."

Mercedes' specific make-up - a fusion of an old English team with increasing levels of German money and expertise imported over the years, with a German and an English driver to match - renders the outfit more susceptible to internal rifts than most. And next season, if Sebastian Vettel's Ferrari is even closer to the leading pace, a feudal relationship between Hamilton and Rosberg could prove fatal.