Nico Hulkenberg topped the times for Williams on the second day of this week's final pre-season Formula 1 test at Barcelona on Friday.
The German toppled local hero Fernando Alonso from the top of the timesheets early in the afternoon during some qualifying simulation work - with a performance that once again shows how hard the formbook is to predict this season.
Hulkenberg had spent the morning on some short runs prior to embarking on a race-type simulation. He completed that without problems - doing 19 laps and then another 27 laps before the lunch break.
In the afternoon, while most other teams focused on race distance simulations, Williams went the other way and embarked on a series of qualifying simulations.
His best time of 1m20.614s was set on the second flying lap of a stint, with rival drivers not able to dislodge him as they focused on race runs for the afternoon.
"We've had a good test here," Hulkenberg said. "P1 today is nice but means nothing, to be honest. We're not in Bahrain yet! It's positive for the team, and for me, to know what the car can do, though.
"We did a lot of set-up work today and have found some interesting things so I feel ready and confident to go to Bahrain now."
Although Hulkenberg's effort denied his Ferrari rival the top time as he rounded off his own pre-season preparation, Alonso will have been far from unhappy about how his day went.
The Spaniard, whose opening day efforts had been disrupted by an electrical problem, completed a varied programme with the F10 to leave his team's rivals in no doubt that Ferrari is in strong shape for the first race in Bahrain.
With Ferrari having brought a raft of aerodynamic updates to the car for this week's test, including a shark-fin engine cover, Alonso spent this morning working through qualifying simulations.
He steadily improved his pace to set a best effort of 1m20.637s on his final low-fuel run - comfortably quicker than Red Bull Racing's Mark Webber had managed on the opening day of the test when his best was 1m21.487s.
Although differing fuel loads and improved track conditions make it hard to judge a true comparison between the ultimate pace of the two title-favourite cars, Alonso's performance will have been a big boost for him.
After spending most of the morning working on those low fuel runs, Alonso did a longer stint before lunch - and then rounded off his effort with a race distance simulation in the afternoon.
He completed that without drama - despite a few red flags caused by rival drivers - but his day came to an early end when he stopped on track with just a couple of minutes of the session remaining.
Pedro de la Rosa signed of his build-up to the new season with another solid day for BMW Sauber. Having focused on the low fuel runs in the morning to set his best lap of 1m20.973s, he completed a race type run - getting down in the 1m22s region towards the end of the stint.
Vitantonio Liuzzi was another driver to complete a race distance for Force India in the afternoon, having spent the morning concentrating on low-fuel analysis to set the fourth quickest time.
Sebastian Vettel improved on team-mate Webber's best time during his first day in action at Barcelona, but the day ended with a mechanical problem while he was undertaking a race simulation in the afternoon.
During morning low-fuel runs Vettel's best had been 1m21.258s, while in the afternoon he did two stints - one of 29 laps and then another 33 before his car stopped on track. His fastest time during these race simulations was in the 1m23s.
Former world champions Michael Schumacher and Lewis Hamilton had fairly low-key outings as they focused on longer runs throughout the day to end the day seventh and eight overall respectively.
Schumacher got to try out a raft of aerodynamic updates to the W01, but opted against chasing low fuel times over the course of the day - a similar tactic adopted by Hamilton.
Robert Kubica was another driver who never made an impression on the timesheets, as he completed 53 laps for Renault to end the day ninth overall on the timesheets. The team had hoped to complete a race distance in the afternoon but abandoned it due to limited running.
In the battle of the new teams, Jarno Trulli ended the day just ahead of the Virgin Racing car of Timo Glock - despite causing two red flags late in the day.
Although Glock ended the day at the bottom of the timesheets, he and his team will have been happy to have got plenty of mileage under their belts.
The team had lost track time on Thursday after Lucas di Grassi's accident but, having flown new spare parts in, it resumed running early in the morning to complete a total of 52 laps.
Pos Driver Team Time Laps 1. Hulkenberg Williams-Cosworth (B) 1:20.614 99 2. Alonso Ferrari (B) 1:20.637 134 3. de la Rosa BMW-Sauber (B) 1:20.973 114 4. Liuzzi Force India-Mercedes (B) 1:21.056 90 5. Vettel Red Bull-Renault (B) 1:21.258 125 6. Alguersuari Toro Rosso-Ferrari (B) 1:21.571 104 7. M.Schumacher Mercedes GP (B) 1:21.689 85 8. Hamilton McLaren-Mercedes (B) 1:22.152 93 9. Kubica Renault (B) 1:24.912 53 10. Trulli Lotus-Cosworth (B) 1:25.524 70 11. Glock Virgin-Cosworth (B) 1:25.942 52 All Timing Unofficial