Lopez wound up third quickest, with both he and fourth-placed Norbert Michelisz opting not to attempt any late improvements.
Nicky Catsburg was sixth for Lada, with Fredrik Ekblom top Volvo in 11th.
In a tight opening session, Monteiro led from team-mate Michelisz after a late improvement.
Monteiro's best time, a 1m22.081s, was just 0.003 seconds faster than Michelisz's, the Hungarian having led his team-mate by a similar margin into the final five minutes of the session.
Lopez prevented a Honda 1-2-3 - having also done so during Friday's test session - with the third-fastest time, just 0.003s faster than Huff.
Thed Bjork was the only other driver to get within a second of the pace in fifth in his Volvo S60 Polestar, ahead of Catsburg and his Lada team-mate Hugo Valente.
Yvan Muller finished the opening session at the back of a tight midfield pack in the second works Citroen C-Elysee, 1.421s off the pace, although the Frenchman did improve his placing in the second session, recording the seventh-fastest time.
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