Force India deputy team principal Bob Fernley expect his outfit and Williams to be "absolutely equal" in the final two races of the 2016 season.
The two teams are still battling for a lucrative fourth place in the constructors' championship, with Force India nine points head of its rival and only Brazil and Abu Dhabi remaining.
And Fernley expects the ultra-close battle to continue, saying the two teams should be evenly matched in the two remaining races.
"I think the last two races are looking absolutely equal between the teams," Fernley told Motorsport.com.
"We thought Mexico favoured Williams, but the next race in Brazil could have variables, so you've always got the opportunity of weather or something like that changing things round a bit.
"Apart from that it's pretty standard, routine racing."
Force India extended its advantage from eight to nine points in Mexico at a venue where Williams was expected to have the upper hand.
Fernley admitted his team did not expect to be able to outscore its rival in the Mexican round.
"It was a long race for one point," Fernley said. "The bottom line is that, between Williams and ourselves, we're fighting for seventh to 10th places.
"Going to Mexico, we probably expected Williams to take seventh, and possibly even eighth, with us ninth and 10th.
"So to come out of Mexico with a point extension on the lead, consolidating what we had, was I think a really, really good result for us. The key thing for us is we came away from there looking very strong."