MONACO (AP) The chummy rivalry between Formula One champions Lewis Hamilton and Sebastian Vettel could be tested at this weekend's Monaco Grand Prix, an unforgiving circuit where drivers are often pushed to the limit.
After five races, four-time F1 champion Vettel is six points clear of three-time champion Hamilton. They have two wins each and are relishing what is, surprisingly, their first championship tussle.
When Vettel was dominating for Red Bull, winning his titles from 2010-13, Hamilton lagged behind with McLaren. As Hamilton started dominating for Mercedes the following year, Vettel struggled with Red Bull. After switching to Ferrari in 2015, the German driver failed to significantly challenge Hamilton or his former Mercedes teammate, Nico Rosberg.
''When he was in the Red Bull car, of course I wished my car was a little bit quicker so I could have given him a battle,'' Hamilton said Wednesday. ''He could say the same thing for the last few years. It doesn't deter from the fact he's an exceptional driver and he continues to show that.''
Although they share a total of 99 F1 wins, this is the first year Hamilton and Vettel have really gone head-to-head on the track.
''You have to respect if other people do a good job,'' Vettel said. ''We're very different. But I think we have a very strong connection.''
The rivalry has been enthralling, and it is a relief for Hamilton to be challenging a driver he respects so much and, additionally, one from another team.
For the past three years, Hamilton was embroiled in a tense fight with Rosberg and their thorny relationship caused friction within Mercedes.
An air of relief has swept through Mercedes since Rosberg retired after winning last year's title. Not because he was unpopular, but because the team no longer has to deal with an ongoing saga that the media feasted on.
''This season I have re-discovered why I love the sport,'' said Toto Wolff, the head of Mercedes motorsport. ''We are in a massive fight with Ferrari.''
In other words, the fight has been taken outside of Mercedes itself.
''There's more passion and excitement being extracted from this team,'' Hamilton said. ''I've never seen so much passion in the years I've been with this team.''
However, an incident in Spain two weeks ago, where Hamilton won ahead of Vettel, showed cracks could start appearing in the smooth facade of their relationship.
Vettel came perilously close to nudging Hamilton off the track as they fought for space heading into a turn. Hamilton had seemed somewhat irked by Vettel's aggression - although it was exactly the kind of in-your-face driving Hamilton revels in.
The psychology factor will, Hamilton said, eventually arrive.
''It is definitely going to be a part of it, for both of us, seeing as it's such a long year,'' he said. ''Just like it is in golf, over 18 holes.''
Hamilton insisted he is tough enough to withstand any pressure Vettel puts on him.
''I take a lot of pride in that I'm very strong mentally. It will be interesting to see,'' Hamilton said. ''I don't have any intention of playing psychological wars outside the car. I want to beat him in the car when he's at his best. That says what it needs to say.''
With the F1 title shaping into a two-way race, neither can afford a slip.
That will increase the pressure on both in glitzy Monaco, where F1 lovers mingle with millionaires.
The smallest braking mistake on a tight and sinewy 3.4-kilometer (2.1-mile) circuit through the winding streets of Monte Carlo, past its famed casino and around its glittering, yacht-laden harbor, can send a distracted driver into the barriers.
''There is no such thing as a low risk lap in Monaco,'' said Red Bull driver Max Verstappen, who crashed in last year's race.
With overtaking notoriously difficult, pole position holds increased value. That makes qualifying crucial, where drivers juggle speed with not pushing the car too hard.
''It is a mentally exhausting weekend,'' Mercedes driver Valtteri Bottas said.
But one advantage for drivers this year is that the Pirelli tires are far more durable, increasing time on track and limiting pit stops.
Still, that advantage is offset by another factor: the size of the cars.
F1 rule changes this year led to cars being made faster and wider. On a narrow track, this poses ''a massive challenge'' when pushing the car close to the limit, Hamilton said.
''It'll be a real test of your awareness of where the car is,'' the Englishman said.