The Argentines, who did not drop a set en route to the final, held their nerves in the key moments, striking returns with great depth and closing the net effectively to triumph after two hours and 21 minutes at the ATP 250 event in Spain.
In a tight second set, Gonzalez and Molteni recovered from squandering a break advantage, before they pulled away from 4/4 in the Match Tie-break to clinch the crown. The pair has now won three titles together across all levels, having won trophies on the ATP Challenger Tour as a team in 2014 and 2017.
The 39-year-old Gonzalez has improved his tour-level doubles finals record to 12-6 with the victory, while the 34-year-old Molteni is now 11-6 in championship matches. Earlier this season, Molteni captured titles with Santiago Gonzalez in Cordoba and Buenos Aires.
Americans Lammons and Withrow were aiming to win their second tour-level title as a team, having tasted success in San Diego last month.