Montecalvo scored the Pro/Am class pole on Saturday but the first race for the duo was ruined by a puncture.
Sanchez made amends on Sunday. After starting 18th, the Mexican earned the award for the best start of the race, moving into the top ten within two laps.
He handed over to Montecalvo at half race distance and the American drove the Always Evolving / AIM Autosport Nissan GT-R NISMO GT3 across the finish line in third place.
However, a penalty applied to the class winner elevated Sanchez and Montecalvo to second.
“We were very unlucky with the flat tyre on Saturday after having started on pole,” Sanchez said.
“We had to recover a lot of positions on Sunday, starting 18th overall and eighth in class. We spent a lot of time discussing the strategy and the plan was certainly to be aggressive on the start.
“I went inside first, then outside and managed to grab eight positions in the first two laps to move into the top 10 and fourth in the Pro/Am class.
“We ended up P2 at the end because the class winner had to serve a drive-through penalty. It was a really good day. We were a little unlucky with the safety car as well. We were right behind the eventual class winner so we came very close to getting the win.”
The final round of the Pirelli World Challenge SprintX Championship will be held at Circuit of The Americas on September 1-3.