The defending champion was never challenged once he was in the lead

The Ducati rider was never seriously challenged after taking the lead on lap eight and cruised home ahead of Spanish duo Jorge Lorenzo and Dani Pedrosa.

Valentino Rossi finished back in fifth place, one ahead of British debutant James Toseland.

It was Toseland's first race after his move from World Superbikes last year.

I felt it would be a hard race - I didn't have a lot of grip at the rear and people were bashing fairings and knocking each other out of the road Race winner Casey Stoner

Toseland finished just 0.7 seconds behind Rossi and admitted he had been "amazed" by his own performance.

"I gave it my best shot. For my first race to be just behind Valentino on the same bike is amazing," he said.

"When the new engine comes we can be more competitive.

"I'm still learning. I made a couple of hard moves but that was a lack of experience at this level on my part.

"I passed Jorge hard and we touched but fortunately he was OK and went on to finish second."

Pedrosa was the race leader in the early stages before Stoner, who started fourth on the grid, managed to impose himself.

606: DEBATE Your thoughts on the race

The style of his victory was reminiscent of his dominance last season, but the Ducati rider told BBC Sport his work had been cut out securing the win.

"It's been a hard weekend for us," said Stoner.

"We didn't start well at all. I felt it would be a hard race - I didn't have a lot of grip at the rear and people were bashing fairings and knocking each other out of the road.

"I was surprised to be up going into the eighth or ninth lap.

"I managed to get in front where I felt comfortable and then do some reasonable lap times."

Qatar MotoGP result:
1 C Stoner (Aus) Ducati 42:36.587
2 J Lorenzo (Sp) Yamaha at 5.323
3 D Pedrosa (Sp) Honda 10.600
4 A Dovizioso (It) Honda 13.288
5 V Rossi (It) Yamaha 13.305
6 J Toseland (GB) Yamaha 14.040
7 C Edwards (USA) Yamaha 15.150
8 L Capirossi (It) Suzuki 32.505
9 R de Puniet (Ff) Honda 33.003
10 N Hayden (USA) Honda 38.354

World championship standings:
1 C Stoner (Aus) Ducati 25 pts
2 J Lorenzo (Sp) Yamaha 20
3 D Pedrosa (ESP) Honda 16
4 A Dovizioso (It) Honda 13
5 V Rossi (It) Yamaha 11
6 J Toseland (GB) Yamaha 10
7 C Edwards (USA) Yamaha 9
8 L Capirossi (It) Suzuki 8
9 R de Puniet (Fr) Honda 7
10 N Hayden (USA) Honda 6

250cc race result:
1 Mattia Pasini (ITA) Aprilia 40:16.202
2 H Barbera (Sp) Aprilia @ 0.557
3 M Kallio (Fin) KTM @ 1.029

250cc championship standings:
1 M Pasini 25 pts
2 H Barbera 20
3 M Kallio (Fin) 16

125cc Grand Prix result:
1 S Gadea (Sp) Aprilia 38 mins 09.444 secs
2 J Olive (Sp) Derbi 38:10.376
3 S Bradl (Ger) Aprilia 38:11.104
4 M Di Meglio (Fr) Derbi 38:11.215
5 S Redding (GB) Aprilia 38:11.263
6 D Webb (GB) Aprilia 38:17.133

125cc world championship standings:
1 S Gadea (Sp) Aprilia 25 pts
2 J Olive (Sp) Derbi 20
3 S Bradl (Ger) Aprilia 16