Romain Grosjean kept Lotus on top of the pile on the second day of running at Catalunya, with a late lap being good enough to ensure he remained quickest in Spain.
The French driver completed more than 120 laps at the wheel of the E20, which included a race simulation during the afternoon. In the closing moments of the day, Grosjean then set a lap of 1min 22.614secs, which put him half a second clear of his nearest rival.
“I'm very happy with the car, and it was great that we could still run strongly at the end of the session, even after a long stint," he said. "At the start of the day we suffered slightly with tyre degradation, but we changed a few things and this improved as the day went on.
"Today was the first race distance I've completed in a long time and I'm feeling pretty good. No doubt my neck will be a little sore tomorrow, but the rest of me is fine!"
That nearest rival was fellow Frenchman Jean-Eric Vergne, who looked set to lead the way for Toro Rosso despite failing to set a lap-time during the afternoon. Vergne had led the way at lunchtime but an engine issue meant he was restricted to pit-stop practice during the afternoon.
Like Grosjean, Sebastian Vettel set his best time during the afternoon to finish third for Red Bull in his first day in the RB8 this week with Fernando Alonso in fourth after a busy day where he completed more laps than any of this rivals.
Heikki Kovalainen was an impressive fifth for Caterham and was within a second of the quickest time prior to Grosjean's late burst. Sauber's Kamui Kobayashi rounded out the top six despite limited running in the afternoon after a hydraulic leak.
“I am pretty happy with the car and its handling under race conditions," the Japanese driver said. "We wanted to improve compared to the last test, and we clearly did that. Obviously we couldn't do everything we had on our programme, but I think we can compensate for that.
"We still have two days of testing left and I'm very much looking forward to being in the car again on Sunday. Of course it is too early to know where we are compared to the others, but the feeling is good."