The race for the 2017 Formula One drivers' championship just got nasty.

What has so far been a rivalry characterised by mutual respect between Sebastian Vettel and Lewis Hamilton took an unsavoury turn in Azerbaijan on Sunday.

As the safety car prepared to pull in ahead of one of three restarts at the Baku City Circuit, Vettel drove into the back of Hamilton's Mercedes, causing damage to both cars.

So irked was the Ferrari driver by what he perceived to be so-called 'brake testing' by the Briton, where a driver deliberately slows down to force another car to brake, he immediately pulled up alongside Hamilton, gestured his dismay, and swerved into the Mercedes, causing a clash of wheels.

Vettel's volatile temper is well known - countless angry radio communications when he feels hard done by are testament to that - but this was on another level.

The German, who just last month described the "strong connection" between himself and Hamilton, played ignorant when informed of a 10-second penalty for dangerous driving, asking his team to tell him when he was alleged to have committed the offence.

As it panned out, the sanction was not as harmful to Vettel's campaign as it could have been - a loose head rest meant Hamilton also had to pit from the lead and the pair finished fourth and fifth respectively, although the three-time champion did voice his displeasure at what he felt was a lenient penalty in the circumstances.

While this may not prove to be the biggest turning point in terms of determining the ultimate destination of the title - Vettel only added two points to his championship lead - it promises to cause a seismic shift in the nature of the contest.

Talk of mutual respect - on Hamilton's part, at least - gave way for inflammatory talk of "disgusting" and "disgraceful" driving in the wake of the race.

"I didn't brake check him at all," protested Hamilton to Channel 4 after a chaotic grand prix that was eventually won by Red Bull's Daniel Ricciardo, ahead of Valtteri Bottas and Lance Stroll. 

"For him to pretty much get away with driving into another driver is a disgrace. I think he disgraced himself today.

"Imagine all the young kids watching today, seeing that kind of behaviour from a four-time world champion."

Hamilton spent much of last season feuding with team-mate and eventual champion Nico Rosberg. It looks as if he'll have to brace himself for another bumpy ride this time around.