The Venezuelan set the early pace and led for the majority of the day, racking up 102 laps in the process. A late change to Pirelli's super soft compound then thrust him to the top, as he worked down to a 1m 24.871s - faster than Lewis Hamilton's pole time, and almost one second better than Nico Rosberg managed for Mercedes.
The German also broke into triple figures on the lap count, while his run included a first trial of the Mercedes' prototype 'megaphone' exhaust. The team removed the device for Rosberg's later runs.
Kimi Raikkonen was third for Ferrari, racking up 94 laps as the team recovered from a disrupted first day in Barcelona. A late run meanwhile lifted the Ferrari-powered Sauber of Esteban Gutierrez into fourth, half a second down the road. The team suffered a brief fire at the rear of the Mexican's car before lunch, but otherwise enjoyed a relatively trouble-free day.
Gutierrez's late run carried him above the Williams of Susie Wolff, who tested the Mercedes-powered FW36 for the first time ahead of her Friday practice debut at Silverstone in July.
Wolff's fastest time, a 1m 27.280s, was set on the soft compound and was enough for fifth overall. She steadily improved throughout the day, with her only mistake coming when she spun exiting Turn 10 early on.
"This was my first opportunity to drive the FW36 and I learnt a lot about how to drive these new look cars which are very different to previous seasons," Wolff said.
"With last year's car the harder you pushed the faster you went, but now you have to manage certain elements a lot more. The cars also have a lot more torque which was a steep learning curve, and this caught me out at the beginning of the session.
"Overall today was a productive day for the team and we worked very well together to quickly complete our planned aero and mechanical evaluations. I was then able to get some good mileage under my belt to understand the characteristics of the car and how to get the most out of this new style of power unit."
Marussia's Jules Bianchi was another late improver, as a final run on the soft compound elevated him into sixth and ahead of the Red Bull of Sebastian Vettel.
The four-time champion suffered a problematic day and did not emerge for the first two hours, with the team subsequently confirming gearbox issues had caused the delay.
Force India's Daniel Juncadella and Toro Rosso's Daniil Kvyat also hit trouble - the former running off at Turn 4, and the latter causing two red flags - on their way to eighth and 10th respectively. Juncadella's day was devoted to tyre development work for Pirelli.
The pair sandwiched Belgian youngster Stoffel Vandoorne, who managed an impressive 136 laps - enough to qualify for a Super Licence - on his F1 debut with McLaren.
"This has been a fantastic day for me: my first experience in a Formula One car, and a really great opportunity to get plenty of laps under my belt," Vandoorne said.
"I want to say a big thank you to the team. It's also great to have been able to contribute to the test programme: 136 laps today was a fantastic achievement, and it's great that it's earned me my F1 Super Licence."
Caterham meanwhile were unable to run at all due to damage following Kamui Kobayashi's crash in the closing stages of day one.
Unofficial Wednesday times from Barcelona:
1. Pastor Maldonado, Lotus, 1m 24.871s, 102 laps
2. Nico Rosberg, Mercedes, 1m 25.805, 102 laps
3. Kimi Raikkonen, Ferrari, 1m 26.480, 94 laps
4. Esteban Gutierrez, Sauber, 1m 26.972s, 85 laps
5. Susie Wolff, Williams, 1m 27.280s, 55 laps
6. Jules Bianchi, Marussia, 1m 27.718s, 55 laps
7. Sebastian Vettel, Red Bull, 1m 27.973s, 73 laps
8. Daniel Juncadella, Force India, 1m 28.278s, 91 laps
9. Stoffel Vandoorne, McLaren, 1m 28.441s, 136 laps
10. Daniil Kvyat, Toro Rosso, 1m 28.910s, 21 laps