Valtteri Bottas' winless year was the only mark against Mercedes in another highly successful year, Formula 1 motorsport boss Ross Brawn has claimed.

The Finn made a strong start to the 2018 campaign arguably beating an out-of-sorts Lewis Hamilton in the early races such were his performances in Bahrain, China and Azerbaijan.

All three races could have been won by Bottas if circumstances had been different but instead, his confidence dropped and much of the year was spent playing the 'wingman' role to his teammate.

“The only slight flaw, if there can be one in a season like this, was the performance of Valtteri Bottas, who had a difficult season, plagued by bad luck,” said the former Mercedes team boss.

“Valtteri had some opportunities to win, but either through misfortune, as in Baku, or due to the occasional, understandable, decision by the team to maximise the result for the benefit of both championships he didn’t manage it.

“The result [was] that he seemed rather out of sorts by the end of the campaign.”

Bottas' run of results in the final races highlighted it with four consecutive fifth-place finishes meaning he became the first Mercedes driver since 2012 to go a full season without a win.

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On the other side of the garage though, it was jubilation as Hamilton secured a fifth world title and the Brackley-based team made it five straight Constructors' titles as Ferrari's challenge faded.

“When you win so much and for so long, it is very easy to fall into the trap of complacency. It’s almost inevitable but can be avoided by consistently raising the bar," Brawn commented.

“Only Ferrari in the Schumacher era has won more than five titles in a row and I had the honour of being technical director of the team when they managed six.

“I recall that every year we were aware that for the following season, we would be starting again from zero, aware that just because we had been strong before, it didn’t automatically translate into an advantage of fractions of a second, because in F1, you can never stop.

“That’s what the team run by Toto Wolff was able to do – avoid panic when it realised that it was not enough to be perfect to beat Ferrari but that more effort would be required than had initially been envisaged.”