Max Chilton in the Marussia car was the surprise leader at the end of Tuesday's test session in Barcelona.
The Brit finished with a time of 1:26.434s, two tenths quicker than Charles Pic in the Lotus F1 car, leaving an unfamiliar look to the timesheets on a track which was drying out.
It was Chilton's stint on the Pirelli supersoft tyre late in the day which gave him the advantage, raising eyebrows throughout the paddock in what is the second of four in-season tests brought in for the 2014 campaign.
Pic in second was on the soft tyre option. He was making his first return to a Formula One car since last season with Caterham as the Lotus F1 test driver and will be pleased with his days work for the team who clearly have an improving car.
Championship leader Lewis Hamilton was third fastest of the day on the medium tyre and completed 79 laps of all important data for the the dominant Mercedes.
The 29-year-old told Sky Sports News: "It is my job to be here and testing is important for the team to get through some things and also to get back into the car after last weekend when I was really uncomfortable in the car and get it comfortable again was important."
Things are not running as smoothly for Ferrari and Kimi Raikkonen. The Finn will have been frustrated to have only completed 20 laps in the session despite posting the fourth fastest time. The 2007 world champion had engine problems before ending up in the gravel as he continues his struggle with Fernando Alonso for equality in the Ferrari team.
Jean-Eric Vergne was fifth fastest of the day for the Toro Rosso team followed by Nico Hulkenburg for Force India. While Felipe Massa of Williams was in seventh ahead of Jenson Button who continues to look for consistent pace in the McLaren car.
Kamui Kobayashi was three-and-a-half seconds behind the lead time in ninth for Caterham F1 with Sebastien Buemi and Giedo van der Garde returning to Formula One with Red Bull and Sauber with test roles.
For Chilton it must have been a great feeling to end the day with the best time. The 23-year-old has impressed in his short time in Formula One having become the first driver in a rookie season to complete every race. He has kept up that record this season, also adding two 13th place finishes which are vitally important for the Marussia team and their end of season standing.
The test will continue on Wednesday as teams look to develop their cars for the upcoming Monaco Grand Prix in just over a weeks time where Lewis Hamilton will be looking to achieve a fifth straight victory.
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