Vettel - currently four points ahead - will start directly behind his fellow German, who is on pole for the fourth straight event. And while the Ferrari star couldn't challenge Mercedes over a single lap in qualifying, he believes they will be far more competitive over the 71-lap race on the Autodromo Hermanos Rodriguez.
"We are here to fight, we have nothing to lose," Vettel said after qualifying. "Nico is the primary target. We want to keep second position in the championship and we'll do everything we can to achieve that.
"On Friday we seemed to be very quick on the long-runs. Obviously it is always difficult to know what other people are doing, but considering that we were on the harder tyre, we seemed to be very quick.
"I hope we can be quick tomorrow as well, and make the tyres last. I think this will be the key for the race because on paper it looks easy, but then, with all the sliding around from low grip surface, we've seen many people struggling to keep their tyres alive. Who knows what happens - I think it should be exciting for all of us."
Vettel has scored podiums in seven of the last eight races, and all of the last five - including victory in Singapore. Rosberg, by contrast, has two podiums from his last five outings, with retirements in Italy and Russia major factors in his current deficit to Vettel in the table.