Marcos Rojo says the 1-1 draw with Liverpool a fortnight ago gave Manchester United a renewed enthusiasm.
The Red Devils almost came away with a surprise win over the Premier League leaders.
They have since beaten Partizan Belgrade and Norwich City, and Rojo says confidence is high thanks to the positive result against their bitter rivals.
"After the Liverpool game, I think the team grew in confidence," he told the club's official website.
"It gave us much more drive and when we went on to get a good result away from home, I think it strengthened our belief and allowed the players to express themselves that bit more, meaning we went back to attacking in the way we usually do."
