Christian Horner reckons Mark Webber's struggles to adapt to Red Bull's late season upgrades cost him last year.
Webber had been leading Red Bull's charge mid-way through the Championship as the Aussie, who had claimed the wins in Monaco and Britain, was second in the standings behind Fernando Alonso.
However, as Red Bull continued to develop their RB8, it was his team-mate Sebastian Vettel who came to the fore, winning four successive grands prix to take the lead in the Championship from Alonso.
Vettel went on to win his third title by three points over Alonso while Webber plummeted to sixth, 102 points off the pace.
"Certainly Seb was able to get more out of the upgrade than Mark was," Red Bull's team boss told Autosport.
"It did seem to suit his requirements whereas Mark never seemed quite as comfortable. But he still had Korea pole, a front row in Abu Dhabi, and outqualified Seb in Brazil.
"It was mainly in the races where Seb was able to exploit the most out of the car."
Horner added that he believes despite Vettel winning three titles on the trot, his two drivers were as evenly matched as McLaren's 2012 line-up of Jenson Button and Lewis Hamilton.
"I think it varies from track to track, condition to condition. In Brazil, between Lewis and Jenson it was swings and roundabouts between different points of the race.
"Some of that is style, some of that is lines used, but the same thing applies as the car develops - one driver will sometimes get more out of it than the other.
"It's obviously tough for Mark - he is a world class driver but he is up against the best in the world. It is hard for any driver to accept that."
