Australia's Casey Stoner celebrates on the podium after winning the Portuguese Grand Prix.

Australia's Casey Stoner celebrates on the podium after winning the Portuguese Grand Prix. Photo: RAFAEL MARCHANTE

World champion Casey Stoner admits he is still battling an arm problem despite the impressive win in Portugal which ensured the best season start of his MotoGP career.

The Honda rider - whose maiden win on the Estoril track means he's now had victories at every Grand Prix circuit - triumphed from 2010 world champion Jorge Lorenzo on Sunday, claiming a one-point lead over the Spaniard after three rounds.

With two wins and a third placing, he's off to his hottest start to a season since he joined MotoGP in 2006.

The 26-year-old also picked up two wins in the first three races on the way to his first MotoGP title in 2007, but failed to finish on the podium in the other.

The success has come despite being affected by ''arm pump'', a condition where the nerves get trapped and numb the hand during races.

''There was a bit of pressure throughout the race,'' Stoner said.

''I wasn't feeling good or comfortable and I had a bit of arm pump.

''I was lucky to hold on and win.''

Stoner's teammate Dani Pedrosa, who became only the seventh rider to celebrate 100 podium finishes as he came third, praised Stoner's ride.

''Casey did a good race, unbelievably strong,'' Pedrosa said.

''It's been a really tough race from the beginning, the pace was very, very high from the first lap to the final one.

''To reach my 100th podium is amazing and shows how fast the time goes.''

Lorenzo, a winner twice in Portugal including his first MotoGP, said he had never felt as if he was going to win.

''To be honest I only ever expected to be at best second,'' said Lorenzo, who had seen his run of four successive poles ended on Saturday when he timed fourth fastest in qualifying.

''We had a lot of problems in practice and we were losing time every lap in the straight. Stoner was very strong.''

Pedrosa got the better start but was quickly passed by both Stoner and Lorenzo while Cal Crutchlow lost two spots and Valentino Rossi, gained two places from ninth to seventh.

With 10 laps to go Stoner and Lorenzo looked to have the race to themselves as Pedrosa dropped off slightly and further behind the field was whittled down with just 16 of the original 20 starters.

Stoner repelled everything that Lorenzo threw at him and going into the final lap held a comfortable lead of just over a second and never looked like relinquishing his advantage.

The Australian overtook Lorenzo on the points table which, after three races, now reads Stoner 66, Lorenzo 65, Pedrosa 52 and Cal Crutchlow 37. AAP-AFP