The Brazilian completed 101 laps of the Spanish circuit in his Ferrari F150, with his best time of 1:20.709 coming early on in the day, almost eight tenths of a second quicker than the Mexican who set his quickest time when the track was at its best.
It was a sold run for PÃƒÂ©rez and while he did stop out on track causing a red flag, it subsequently turned out that his team had elected to run out of fuel.
Mark Webber finished third fastest in the RB7, less than one tenth slower than PÃƒÂ©rez, as the team concentrated on longer runs, with positive results and consistent lap times.
The average pace was in and around the 1:23 mark, a time Ferrari and Red Bull appeared to manage comfortably during long run outs, while McLaren went between 1:23 and 1:24.
Toro Rosso reserve driver Daniel Ricciardo showed his credentials for a future F1 drive by securing fourth place in the STR6 during the morning session with a time of 1:21.755.
Lewis Hamilton was fifth quickest with a 1:21.914 as McLaren shook down the MP4-26 without ever really pushing it too hard, the real purpose of the day to check everything was in working order and HamiltonÃ¢â‚¬â„¢s fastest time came on a single-lap run, showing that more is still to come from the new car.
Adrian Sutil was seventh quickest in the VJM04 as Force India also shook down their 2011 challenger, ahead of a more extended test programme on Friday. The German completed just 28 laps after losing several hours to early problems with exhaust blast shields, but once the issue had been resolved, the car was able to complete its baseline runs, and Sutil is confident the car is much better than its predecessor.
With Robert Kubica absent due to the injuries sustained in a recent rally event in Italy, Vitaly Petrov led the testing for Renault, finishing eighth quickest in the R31 after regularly lapping around 1:24. His quickest time, a 1:23.504, was four tenths quicker than MercedesÃ¢â‚¬â„¢ Nico Rosberg in the W02.
Mercedes times varies by almost two seconds between 1:24 and 1:26 as the team worked on different fuel loads, with RosbergÃ¢â‚¬â„¢s quickest time coming on lap 3 of a 17 lap run, while a gearbox problem could be an early concern for the team.
In a disappointing day for Williams, Pastor Maldonado could only manage 13 laps due to a problem with the carÃ¢â‚¬â„¢s rear wing actuator, eventually setting a quickest time of 1m34.968, almost 10 seconds slower than the MVR-02 of VirginÃ¢â‚¬â„¢s Timo Glock, which was another car being shook down for the first time this year, and not a true indication of WilliamsÃ¢â‚¬â„¢ pace.
Trulli consistently lapped in the 1:25 range, and never looked like threatening to improve as he recorded a quickest time of 1m25.086s.
Hispania Racing are the only team not testing in Jerez this week, instead opting to take part in a filming day for tyre manufacturer Pirelli at Monza at the beginning of next week.
MORE: The latest football news
MORE: The latest tennis news
BIOGRAPHY: Ethan Hazard
BIOGRAPHY: Daniel Sturridge