(CNN) -- Triple world champion Sebastian Vettel led a Red Bull one-two in practice for the Hungarian Grand Prix Friday as Mercedes struggled with new tires and the blistering heat in Budapest.
Vettel was fastest on Pirelli's soft offering in the morning and repeated the trick in the afternoon on mediums with teammate Mark Webber just behind.
Mercedes pair Lewis Hamilton and Nico Rosberg have dominated practice and qualifying in recent races, but were off the pace this time in sixth and seventh place respectively in the afternoon runs.
The team had been excluded from last week's tire testing at Silverstone and have catching up to do admitted Rosberg.
"We know it's quite challenging for our car in these hot conditions," he told the official F1 website.
"Some of the other teams look quick here, so we have more work to do," added the German.
Hamilton, a three-time winner at Hungaroring, was more upbeat. "We can generally pull out a bit more in qualifying so let's see how tomorrow goes."
Vettel is seeking his first win in Hungary to follow a maiden triumph in Germany in the previous round and all the omens look good for the German star.
"It's nice when you feel in control of the car and you can play around. I think the car suits the track.
"There is still a bit of work to do, but we need to make sure we get everything out of the car tomorrow," he added.
Webber, who will retire at the end of the season, was just 0.044 seconds adrift of his teammate with Romain Grosjean third fastest for Lotus.
Two-time champion Fernando Alonso and his Ferrari teammate Felipe Massa, who sustained life threatening head injuries in a freak accident at the circuit in 2009, were fourth and fifth quickest.
Kimi Raikkonen made contact with the McLaren of fellow ex-world champion Jenson Button during the session and finished eighth fastest.
Button finished just behind him, a boost for his struggling team with the Force Indias of Adrian Sutil, taking part in his 100th grand prix, and Paul di Resta next.
Saturday will see final qualifying with track temperatures expected to remain over 40 degrees Celsuis for Sunday's race proper.