Testing times for Mercedes pair in F1

PARIS (AP) At last, Formula One has a heated rivalry again. Better still, it's in the same team and there are 13 races left for it to develop.

The dominance of Mercedes, which has swept all six races and all six pole positions so far, prompted fears that this season was becoming even more predictable than the last, when Sebastian Vettel won the final nine races and Red Bull crushed everyone.

Then, at last weekend's Monaco GP, a feud erupted out of nowhere between Mercedes drivers Lewis Hamilton and Nico Rosberg to add some much-needed spice to a dull campaign.

Hamilton has won four races this season, but Rosberg captured Sunday's race from pole for his second victory and reclaimed the overall championship lead with 122 points to 118 for his teammate.

''We're fierce competitors, so you can never expect us to be best friends and compete as fiercely as we do,'' Hamilton said after the Monaco GP. ''But I will try to remain respectful.''

Hamilton ignited the row by taking the brash step of publicly claiming that Rosberg, the son of former F1 champ Keke Rosberg, has less hunger than him after growing up in the luxurious environment of Monaco. Rosberg didn't respond to those claims verbally, but in the eyes of Hamilton he responded to them on the track by making a surprising last-gasp mistake in qualifying that led to a yellow flag. The session was abruptly halted, ending any hopes that Hamilton, at full throttle just behind, had of winning pole.

The fallout escalated quickly.

An incensed Hamilton insinuated that Rosberg - cleared by stewards of any wrongdoing - had done it on purpose, suggesting he would watch his own back the way the late Ayrton Senna did when he fell out with Alain Prost when they drove for McLaren in the late 1980s.

With tensions running high, the two Mercedes drivers were not in the post-qualifying team meeting together and were at opposite ends for the traditional pre-race jaunt around the circuit.

After Rosberg's win, there was no handshake from Hamilton, who came in second to give Mercedes a fifth straight 1-2 finish.

There have been fiery team rivalries before, notably the one between Vettel and Mark Webber at Red Bull. That got very bitter, with each driver ignoring team orders to let the other one pass and making blunt comments about the other.

But the crucial difference is that, apart from 2010 when Webber challenged for the title, the four-time defending champion Vettel was always winning. Relations were ice-cold, but there also seemed to be a mutual acceptance they would never get along and the professional working environment within Red Bull continued to operate smoothly.

The matter is more delicate for Rosberg and Hamilton because they've known each other for such a long time, racing karts against each other and even going on holiday together - something that was never going to happen with Webber and Vettel, and even less so with Senna and Prost.

Rosberg is less experienced than Hamilton, with five GP wins compared to Hamilton's 26, but the German has shown real consistency with top-two finishes in all six races.

Hamilton would still be ahead, though, but for the engine failure that forced the British driver to retire in the season opener at Melbourne. That technical glitch, on what is the most reliable car in F1, likely still rankles him.

After several frustrating seasons with McLaren, Hamilton has a great chance to win his second F1 title six years on.

But standing in his way is his childhood friend.

That relationship is going to be severely tested and the spotlight will be beaming straight in the face of both drivers at the Canadian GP in two weeks' time.