Barry scored in stoppage-time to secure a 1-0 win over a stubborn Reading side on Saturday before United dropped two points with a 1-1 draw at Swansea on Sunday. England midfielder Barry, 31, acknowledges that United's home games against Newcastle and West Bromwich Albion over the Christmas period are easier than City's trips to Sunderland and Norwich.
But City overturned United's eight-point lead in the final six games of last season to win the Premier League title and Barry is adamant Mancini's side have a similar determination this time around. "When there's a little gap it's important that you don't slip any further behind," Barry said. "If we can keep chipping away hopefully we can be there at the end of the season.
"It's going to be a big Christmas and looking at the fixtures, they didn't fall that kindly for us, with two away games with the distances we've got to travel. "They're tough games but we showed a great performance at Newcastle and we've got to do the same over Christmas." City captain Vincent Kompany was on the bench for the win over Reading after a groin problem and he may be fit enough to return to the starting line-up at the Stadium of Light.
Italian striker Mario Balotelli could return from illness, while Mancini will be hopeful that left-backs Gael Clichy and Aleksander Kolarov can overcome minor injury problems. But Samir Nasri, Micah Richards and Jack Rodwell are all ruled out until the new year. Although United have the advantage at present, City's recent defeat to Alex Ferguson's side was their only loss in the Premier League this season and Ivory Coast defender Kolo Toure believes the champions have already demonstrated they have what it takes to retain their title.