The Mexican's 1m21.848s lap on Wednesday edged out Fernando Alonso and Ferrari's Thursday benchmark by 0.027 seconds.
The test's quickest times all came from short one-lap runs on soft tyres, although with varying fuel loads and track conditions involved, they cannot be seen as a definitive measure of qualifying-pace.
Nico Hulkenberg continued Sauber's strong winter pace in third, while Lotus showed well as Romain Grosjean and Kimi Raikkonen took fourth and seventh on combined times, despite a lot of mechanical gremlins for the Finn.
As ever, Red Bull was coy in testing and rarely appeared to run light fuel. Sebastian Vettel and Mark Webber were fifth and 13th.
The drivers' mileage stats were misleading. Alonso led the way with 283 laps, but had three days of running in exchange for missing Jerez earlier in the month.
Max Chilton's second place came by virtue of him getting all four days in Luiz Razia's absence. Marussia actually completed least mileage of all 11 teams.
The top team tally was Williams's 367 laps, four more than nearest rival Ferrari. That came despite Williams being the only team giving a brand new car its debut, having using 2012's FW34 at Jerez.
Drivers Valtteri Bottas and Pastor Maldonado were thrilled with the FW35's immediate reliability.
Of the potential title contenders, Lotus had the most technical issues.
Grosjean was relatively untroubled, getting in 160 laps across Thursday and Friday. But team-mate Raikkonen only managed 87 in his two days, losing much of Tuesday to data-logging problems and nearly all of Wednesday to a gearbox change.
AUTOSPORT special testing coverage:
Gallery Testing blog Technical blog Live commentary Trackside analysis