Christian Horner has warned against underestimating Jenson Button who he believes will fight for this year's World title.
Button is entering his fourth season with McLaren, however, it's his first as the Woking outfit's unofficial number one.
With Lewis Hamilton joining Mercedes, McLaren have drafted in the relatively inexperienced Sergio Perez as Button's team-mate.
However, it is how Button performed when Hamilton was his team-mate that has most impressed Horner.
"Probably to everybody's surprise Jenson went to what was perceived as Lewis's team and he did give them something to think about," the Red Bull team boss told The Guardian.
"The team went from Lewis's team pretty much exclusively - Jenson was the driver, certainly in 2011, that seemed to have the upper hand. The two of them seemed very equally poised throughout last year.
"Jenson is a pretty shrewd operator and probably knew that in terms of out-and-out pace he wasn't as quick as Lewis. But by using other skills that he had, he knew he could compete and beat him.
"He certainly seemed to morph the team around him and it will be interesting to see [what happens] this year as he is very much the de facto team leader."
Horner also revealed that Button enquired about a Toro Rosso drive in 2008 but instead went on to race for Ross Brawn, winning the 2009 Drivers' Championship.
"Jenson has impressed me enormously since that difficult year where he didn't know whether he was going to have a drive or not after Honda pulled out [in 2008].
"I remember his management were asking us even whether Toro Rosso had a drive in the winter of 2008. He came back and delivered in 2009 and then jumped ship [to join McLaren]."
Pressed as to whether Button will be a title contender this season, Horner said: "If the car suits his requirements then there is no reason why not. He is certainly a driver that we do not underestimate."
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