• Casey Stoner leads from start to finish at Phillip Island
• Jorge Lorenzo has plastic surgery on finger

Casey Stoner wrapped up the MotoGP world title with victory in his home event at Phillip Island on Sunday.

The Australian, already confirmed on pole position, was left needing only a top-six finish after the pre-race withdrawal of his title rival Jorge Lorenzo, who suffered a serious finger injury when crashing in the warm-up, and Stoner rode flawlessly to keep himself out in front, taking victory with Marco Simoncelli second and Andrea Dovizioso third.

It was Stoner's second MotoGP title – the first coming in 2007 – and came on his 26th birthday. The win represented Honda's first rider's title of the 800cc era.

Stoner was delighted with an almost flawless race, telling autosport.com: "I don't think I can fit too many more things in today. It's my second title, my fifth win [at Phillip Island] and my birthday too. Home grand prix … everything.

"To win like this is something special. I don't think people can align things to fit in like that. It's been a dream season really. We've had a few ups and downs, but the downs haven't been that far down and the ups have been a long way up, so a big thanks to the team and everyone that's done such an amazing job.

"The race threw a few curve-balls in. Being in the lead, I was the one having to test all the conditions first, and you're never quite sure what's going to happen there.

"It wasn't the way I wanted to do the race. I hoped it would go a lot more smoothly, but we managed to bring it home for the win. Words can't describe how I'm feeling right now."

Lorenzo was rushed to a Melbourne hospital for emergency plastic surgery after one of his fingers was severely injured. The former champion crashed at the exit of turn 12 on his final lap of the 20-minute session, high-siding off the bike and coming to rest on the edge of the circuit.

He walked away from the site shaking his hand and was ruled unfit to start the race by the circuit's medical centre. "When I saw Jorge's crash I thought it was just a small crash," Stoner said after his victory.

"I thought it might be just a small graze or something like that. Then I saw the replay and saw what actually happened and everyone was out there looking for the end of his finger. And it sort of made me feel a little bit sick because I'm a racer, I know what it's like to go through these things and you can't really wish them upon anyone."

A team spokesman said later that Lorenzo had not lost part of his finger in the crash, but that the top of his finger was badly injured and the full extent of the injury would not be disclosed until after the surgery on Sunday night. "He is currently undergoing surgery … We will release a statement once we have a full medical report," he said.

Stoner had led from start to finish, ensuring he kept out of trouble as an eventful race unfolded behind him. Ducati's Nicky Hayden surged to second by the first corner but was soon overhauled by Gresini Honda's Simoncelli, the factory Honda pair Dovizioso and Dani Pedrosa, and Alvaro Bautista of Suzuki.

Valentino Rossi crashed out with 14 laps remaining on the other Ducati after a rash move to pass Bautista, but when rain arrived in the latter stages of the race things were shaken up.

Simoncelli and Pedrosa both exercised far too much caution, allowing Dovizioso to pass the former for second place while the Spaniard was unable to make further headway from fourth.

Bautista, Cal Crutchlow, Hiroshi Aoyama and Karel Abraham all crashed out in the wet conditions as only 10 bikes finished the race. Colin Edwards (Tech 3 Yamaha) was fifth of those, ahead of Pramac Ducati's Randy de Puniet, Hayden, Toni Elias (LCR Honda), De Puniet's team-mate Loris Capirossi – who, along with Hayden, switched to his wet bike – and Karel Abraham of Cardion AB Motoracing.

Stoner also helped his team clinch the constructors' title and the Honda Racing president Tetsuo Suzuki said: "It has been five years since we won our last championship and I am honoured to see that HRC is back and stronger than ever."