Williams driver Felipe Massa believes Ferrari's tyre affinity was the biggest factor in its Malaysian Grand Prix success, but admitted the Scuderia has improved more than its Formula 1 rivals.
At Sepang last weekend Sebastian Vettel clinched Ferrari's first F1 victory since 2013, ending a run of 30 races without a win - the team's longest drought for 21 years.
Williams had no answer to Ferrari's pace, with Massa finishing sixth, one place behind his team-mate Valtteri Bottas, as the Ferraris and Mercedes pulled clear at the front.
Massa thinks Ferrari's key advantage in Malaysia was how well it worked the weekend's Pirelli compounds in the heat, rather than its car being comprehensively better.
"They had a much better car [in Malaysia] and they have much better pace," said the Brazilian.
"They use the tyres in the much better way.
"In Malaysia, everything was related to the tyres.
"I think it's the tyres because why were they not pole position in the qualifying [if the Ferrari was fastest]? Well, they almost were in the rain but in the dry they were slower.
"It's more related to how they use the tyres, I think - or I hope - anyway."
Williams was the second fastest car on outright pace towards the end of last season, behind Mercedes, with Red Bull third and Ferrari only fourth.
"They've made a good car," said Massa of his former team.
"They've improved. I would say Ferrari did a good job, they have improved more than anybody."
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