Hartley retires from Mexican GP, Hamilton wins F1 title

A second power unit failure in as many days has cut Brendon Hartley's Mexican Grand Prix campaign short. 

The Kiwi's Renault expired on lap 33, forcing him to peel off the circuit with smoke and a minor fire leaking from the back of his Scuderia Toro Rosso. 

The race had been a promising one for the Kiwi. Having started from 17th following his qualifying penalty, he improved to 13th by lap six. This was largely thanks to a chaotic start that had claimed Sebastien Vettel and Lewis Hamilton. 

Vettel had won the jump off the line, only to have first place stolen from him by a brave move around the outside at turn one from Max Verstappen.

They exchanged contact, with Hamilton repeating the motion on the following corner while trying to pass both Verstappen and Vettel. Further contact between the two further damaged the Ferrari's wing, and also caused a puncture for the series leader.

This forced them both to lose time and pit at the end of the lap. Felipe Massa and Dan Ricciardo also made an early unscheduled stops — Ricciardo's resulting in a DNF. 

By lap 30, Hartley was up to 12^th following another failure (this one concerning Nico Hulkenberg) and a pass on Haas driver Romain Grosjean. But, it was all cut short by the lap-33 failure. 

Attention turned to Verstappen's hold of the lead, and Vettel and Hamilton's dual recoveries from down the order. The German ace was on fire; setting and resetting the lap record several times on his way to finishing fourth behind winner Verstappen, and podium-getters Bottas and Kimi Raikkonen. 

But, Hamilton's fight to a final position of ninth was enough to seal him his fourth Formula 1 world title. He joins Sebastien Vettel and Alain Prost on the all-time champion list. Only Michael Schumacher and Juan Manuel Fangio have more titles to their name; seven and five respectively.