Paul Hembery has denied speculation that Mercedes' Hungarian GP triumph was thanks to Pirelli's new tyres.
Lewis Hamilton claimed his first grand prix win as a Mercedes driver last time out with his victory coinciding with the introduction of the new Pirellis.
The 28-year-old dominated the race on the new tyres, which feature last year's construction with this year's compounds, starting from pole position and racing through to the chequered flag.
It was an unexpected win for Mercedes who have in the past struggled with their tyres in the heat.
Hembery, though, insists the win had nothing to do with the changes and everything to do with Mercedes' own progress.
"[It's] something they have done," the Pirelli motorsport director told Autosport.
"We were looking at race [and] just waiting, thinking at some stage it would be a problem, but it wasn't.
"It was a surprise to us. It was hot for everybody, everyone was suffering.
"It was all about temperature going in, nothing to do with the tyre; it was the heat going into the tyre - you can do what you want with the tyre, it doesn't affect the heat going in."
The Pirelli boss added that he expects Mercedes will be a "major" competitor in this year's Championship if they continue with their current form which saw them win three of the last five grands prix.
"They obviously have a lot of pace, as soon as everything clicks they were going to be a very competitive act.
"In Hungary it worked and we will see how they go in Spa.
"If they do get that consistency with the pace they have shown then they will be a major competitor."