Kevin Magnussen set the pace for McLaren on the opening day of Formula 1's final young driver test of the year in Abu Dhabi.
The 20-year-old Dane worked his way down to a 1m42.651s in the morning, edging out Red Bull's Antonio Felix da Costa by just over six hundredths of a second.
The pair finished more than three quarters of a second clear of the field, which was headed by Gary Paffett - the McLaren test driver having taken over from Magnussen for the afternoon.
The Briton focussed primarily on trialling a variety of aerodynamic and suspension developments intended for use either in the final two races of this season or on McLaren's 2013 car.
Robin Frijns, this year's Formula Renault 3.5 champion, finished fourth fastest for Sauber. The 21-year-old Dutchman is set for a long-term future with the team.
Nicolas Prost (Lotus) finished fifth fastest ahead of Luiz Razia (Toro Rosso) and Giedo van der Garde (Caterham), who spent the day working on aero developments rather than chasing laptimes.
Razia brought about the day's only red flag 10 minutes from the finish, although he was able to return to the pits under his own power.
Magnussen will return for the final afternoon of the test with McLaren on Thursday, while da Costa - the busiest man on the opening day with 79 laps completed - will remain with Red Bull for one more day before handing the RB8 over to Frijns.
In the Dutchman's stead, Esteban Gutierrez will take over at Sauber for days two and three.
Pos Driver Team Time Laps 1. Kevin Magnussen McLaren-Mercedes 1m42.651s 40 2. Antonio Felix da Costa Red Bull-Renault 1m42.717s + 0.066s 79 3. Gary Paffett McLaren-Mercedes 1m43.407s + 0.756s 44 4. Robin Frijns Sauber-Ferrari 1m43.775s + 1.124s 78 5. Nicolas Prost Lotus-Renault 1m44.194s + 1.543s 55 6. Luiz Razia Toro Rosso-Ferrari 1m44.691s + 2.040s 67 7. Giedo van der Garde Caterham-Renault 1m45.936s + 3.285s 57
*All timing unofficial