After taking a two goal lead in their English Premier League match against Fulham on Saturday, Manchester City were clawed back to level terms before second half substitutes Jesus Navas and James Milner went on to secure a 4-2 win.
Following the game, Pellegrini confessed his side had gone flat in the second half and needed a change, and he thanked his substitutes for that inspiration.
Yaya Toure and Vincent Kompany gave City a 2-0 half-time lead, but Kieran Richardson and a bizarre Kompany own goal made it 2-2 after 70 minutes.
Substitutes Navas and Milner then sealed the win for City, with two late goals five minutes apart.
“I thought that we had to change something,” said Pellegrini.
“When we were winning 2-0 we were still playing well, but we still had a lot of fortune.
“When we were 2-2 I thought that I must change something because I thought we were not going to win the way we are playing.
“Our creative players were tired, so we have an added option.
“Milner gives another style of play, but scored an important goal for the win.”
Pellegrini has been impressed by his side’s form of late, highlighting the improvement in their away form which has seen them win not only in the league, but in the Capital One Cup and the Champions League as well.
“There are a lot of reasons why you can win or you can lose away or at home,” added Pellegrini.
“I think it is important for this team not to be overthinking that we cannot win away because we won two games in the Champions League, won two games in the Capital One Cup, and from the last three games we've won two and drawn one playing away.
“Maybe it's impossible to play exactly the same as we do at home, but I think that it's improving and that's why we are winning.”
City are next up against League leaders Liverpool on Boxing Day, December 26, and Pellegrini admits it is a massive game.
“I think it's a massive game for both Liverpool and for us,” said the Chilean.
“We hope we can continue playing excitingly and scoring the same amount of goals that we are doing at home.”