F1 2015 rookie Felipe Nasr expects things to get more difficult for Sauber as the season progresses.

Nasr has already managed two points' finishes this year, with a fifth in Australia and an eighth in China, but knows the Swiss-squad needs to capitalise on its early season-form and reliability before the likes of Red Bull and McLaren step up.

"I'm quite happy with it," Nasr replied when quizzed about the opening phase of the season. "It's been a good first four races. We have been maximizing our opportunities in these early stages of this championship, but I expect things to become more difficult as we move on. We know our limitations; we know what we can do.

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"So far I think the team gave me enough preparation and I think I was ready to take those chances early on."

Looking to this weekend in Spain, he is optimistic about what the team can achieve.

"Barcelona is always a good picture to see where everybody is sitting and it's not going to be any different I would say in the way that we are also bringing a few updates on the car but we don't know how big is this step compared to our main competitors and we just have to capitalise on these opportunities we have when they show up.

"It's never easy to be in those points, so any points really matter for us. Let's see. We were quite good in testing here in Barcelona, so it's one for me to look forward to," concluded the Brazilian.