Roberto Mancini's side are in the midst of a three-match winless streak in the Barclays Premier League. That drop in form has seen Manchester United build a 12-point lead at the top, while also allowing Chelsea to move within four points of second-placed City.
The Blues could narrow that gap further with victory at the Etihad Stadium on Sunday - something Ba believes they are well placed to do, and he said: "The gap is very big (between United and City) and we have in our head if we win we can get very close to them."
He added: "We know this is not the best time for Man City at the moment and we're going to try and take advantage of that. It is going to be difficult to catch Manchester United because they are so many points clear from City.
"I don't see them losing that many points but we're just going to try and win the maximum possible and see where we will be at the end of the season."
Chelsea head into the match on the back of Thursday night's 1-1 draw with Sparta Prague, which set up a Europa League last-16 tie with Steaua Bucharest.
Manager Rafael Benitez chose to rest several players for the Czech side's visit, with Frank Lampard and Branislav Ivanovic left out of the squad completely.
Ashley Cole and David Luiz were unused substitutes at Stamford Bridge, leaving the latter feeling refreshed ahead of Sunday's match.
"We can put pressure on City," the Brazilian said. "It is a big, big game. If you beat big clubs you take more confidence so this is the objective.
"I want to win against Man City always. That is my mentality. Chelsea's mentality is to get three points."
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