Lopez produced his quickest time of 1m31.227s within the final two minutes of the half-hour test to demote fellow Citroen driver Sebastien Loeb from the top of the timesheets by 0.138s.
Former TC2000 champion Lopez had set the initial pace thanks to a time of 1m32.158s.
It took the Argentine's team-mates until approaching the final third of the test to offer a response, when Loeb found in excess of a one-second improvement over his previous best time.
Zengo Motorsport's Norbert Michelisz spilt up the C-Elysee trio, completed by Yvan Muller, and took top non-Citroen honours in third with two minutes left on the clocks.
The Honda driver ended the afternoon 0.908s adrift of Lopez's benchmark.
Fresh from his maiden WTCC podium in Marrakech, fast improving Frenchman Hugo Valente also caused a late upset to mix it with the Citroens in fourth.
Reigning WTCC champion Muller was fifth, ahead of last year's Superstars champion Gianni Morbidelli.
Former grand prix driver Morbidelli is hoping to kick-start his WTCC comeback at Paul Ricard, having been forced to start from last on the grid in Morocco owing to a practice accident involving Gabriele Tarquini.
Tiago Monteiro was leading works Honda racer in seventh. Team-mate Tarquini's first 2014 Civic WTCC TC1 was destroyed last week when it was T-boned by Morbidelli.
The Italian's replacement machine was only completed on Thursday, but allowed him to take 10th fastest.
"The car was built up using the shell of our test car," explained Tarquini. "It was a great effort and the work only finished yesterday, but of course now we don't have a spare car."
Pos Driver Car Time Gap Laps 1. Jose Maria Lopez Citroen 1m31.227s 11 2. Sebastien Loeb Citroen 1m31.365s +0.138s 12 3. Norbert Michelisz Zengo Honda 1m32.135s +0.908s 15 4. Hugo Valente Campos Chevrolet 1m32.158s +0.931s 11 5. Yvan Muller Citroen 1m32.383s +1.156s 12 6. Gianni Morbidelli Munnich Chevrolet 1m32.704s +1.477s 13 7. Tiago Monteiro Honda 1m32.725s +1.498s 11 8. Tom Chilton ROAL Chevrolet 1m32.954s +1.727s 14 9. Dusan Borkovic Campos Chevrolet 1m32.957s +1.730s 12 10. Gabriele Tarquini Honda 1m33.030s +1.803s 8 11. Mehdi Bennani Proteam Honda 1m33.051s +1.824s 13 12. Rene Munnich Munnich Chevrolet 1m33.762s +2.535s 13 13. Rob Huff Lada 1m34.040s +2.813s 11 14. James Thompson Lada 1m34.444s +3.217s 14 15. Mikhail Kozlovskiy Lada 1m35.395s +4.168s 15 16. Franz Engstler Engstler BMW 1m36.895s +5.668s 14 17. Pasquale di Sabatino Engstler BMW 1m38.212s +6.985s 11 18. John Filippi Campos SEAT 1m39.420s +8.193s 12
Volvo gave the World Touring Car Championship a major boost when it announced it would enter the series, but its ambitions don't stop there. JACK COZENS examines its programme, the S60 and what its arrival means for the WTCC
The 2012 World Touring Car champion says he never had the money to race cars. Yet 2015 is his 11th season in the WTCC. He talks STUART CODLING through his journey from motorsport fan to paid professional - for little more than £100,000