Felipe Massa says Williams seems to have lost some of its straight-line speed advantage this season, particularly in comparison to Ferrari.

Massa lost out to the Ferrari of Sebastian Vettel in Australia two weeks ago in the fight for third and the Brazilian is fearful now that this might cost them in the battle for supremacy with his former team.

"I think the only area that we see that we don't have an advantage anymore is on the straight," Massa told reporters on Thursday ahead of this weekend's Malaysian Grand Prix, round two in F1 2015. "The only thing that Ferrari shows that they have improved massively is the engine - they have a much better system, a much better engine compared to last year, so last year we had a car that we were losing in the corners, we had less downforce than Ferrari, but we were gaining on the straights.

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"For sure, this year the car is much better in terms of downforce and better in the corners, so we already finish in a good way, but how we start we are losing massively.

"We were compensating the speed, we were gaining on the straight, but this time we don't have this difference on the straight anymore. We need to work as strong as we can because we are fighting with a top team that has a big possibility financially to develop the car. I am really thinking we can do it though."

Quizzed on what might have made the difference in Australia, in terms of beating Vettel, Massa said the fact team-mate Valtteri Bottas could not start was key.

"Yes, having two cars!" he confirmed.

"The only [other] thing that was not nice was to leave the pits and to get [Daniel] Ricciardo in front in the place where I didn't have DRS to pass him. I think that was the only thing that put me behind Sebastian, so without the problem I would have been in front.

"He had a little bit extra ace but I don't know how easy it would have been to pass me on the track."

So where has Ferrari improved?

"Maybe they have a better chassis but I would say it is more the engine," Massa continued, "if you see how they finished the season [and] how they started this season, I would put a lot more on the engine."

Meanwhile, Massa said the dominant performance of the Mercedes' was only to be expected.

"It wasn't shocking because they had an amazing advantage last year, but for sure when I see the difference of something like that, you know that to win a race something needs to happen, or they need to have a problem."