The Mexican, who has moved from Sauber to replace 2008 champion Lewis Hamilton at the team, completed 97 laps - nearly one-and-a-half times the Spanish Grand Prix race distance - with a best time of one minute 21.848 seconds on the soft tyres.
Perez did a series of shorter runs in the morning and then longer ones in the afternoon focusing on familiarising the driver with systems and procedures including the cockpit switches and radio messaging.
Red Bull's triple world champion Sebastian Vettel had been the fastest before lunch, although testing times must be treated with caution since teams are working through different programmes, but was forced to end his session early.
"We had some issues with reliability today and we couldn't do as many laps as we wanted," said the German, who was still second fastest overall (1:22.197) and did 84 laps. "It was nothing disastrous, just small things that hampered us today."
The team's race engineering coordinator Andy Damerum said the problems would be resolved by the start of Thursday's session with Australian Mark Webber.
"The stops we had today weren't too serious...we know where the issues are," he added.
Kimi Raikkonen was third on the timesheets for Lotus (1:22.697) although the 2007 champion was sidelined for much of the morning and part of the afternoon by a gearbox problem.
Hamilton, now with Mercedes, was fourth fastest in 1:22.726 after completing a whopping 121 laps - the most of any driver - with his best lap set on the hard tyres in the morning.
"We had a good day and it was nice to get so many laps in," said the Briton. "We're making continual steps forward in terms of our understanding of the set-up and the tyres.
"The guys are working really hard both here and at the factory and it's encouraging to see the amount of work that's being put in. We're focusing on our own programme and just getting on with it."
Ferrari's Fernando Alonso was fifth fastest.
The second test of the pre-season ends on Friday. The first race is in Australia on March 17.
Pos Driver Team Time Gap Laps
1. Sergio Perez McLaren 1m21.848s 97
2. Sebastian Vettel Red Bull 1m22.197s +0.349 84
3. Kimi Raikkonen Lotus 1m22.697s +0.849 43
4. Lewis Hamilton Mercedes 1m22.726s +0.878 121
5. Fernando Alonso Ferrari 1m23.247s +1.399 76
6. Valtteri Bottas Williams 1m23.561s +1.713 98
7. Daniel Ricciardo Toro Rosso 1m23.718s +1.870 70
8. Paul di Resta Force India 1m23.971s +2.123 62
9. Nico Hulkenberg Sauber 1m24.205s +2.357 88
10. Max Chilton Marussia 1m25.115s +3.267 67
11. Charles Pic Caterham 1m26.243s +4.395 102
- Sports & Recreation
- Motor Racing
- Lewis Hamilton
- Sebastian Vettel
- Red Bull