Pep Guardiola had no doubts about handing Tommy Doyle his Manchester City debut on Wednesday night as the 18-year-old impressed in a 3-1 Carabao Cup win over Southampton.

Nicolas Otamendi opened the scoring before Sergio Aguero marked his 350th City appearance with a brace, but in a relatively routine win for City against a Southampton side still reeling from Friday's 9-0 home defeat to Leicester, Doyle looked composed in an unfamiliar role.

The teenager, grandson of City greats Mike Doyle and Glyn Pardoe, was deployed in the centre of a midfield three and, though not naturally a holding midfielder, kept things neat and tidy.

Southampton did not manage a shot on target until the 65th minute, showing life late on with Jack Stephens heading in a 74th minute consolation.

"Tommy played well in a position that isn't his natural position," Guardiola said. "Usually he is further forward. He played really good, so congratulations to him on his debut."

Guardiola turned to Doyle with Ilkay Gundogan given a much-needed night off. With Rodri injured and Fernandinho, deployed in defence this season, suspended, Guardiola said he had little option, but also a trust in Doyle.

"I didn't have another alternative, but he was with us in the pre-season and I saw him a few times in the academy, and I didn't have any doubts he would play to a good level," Guardiola said.

The win was City's 14th in a row in the competition. Having lifted the trophy in each of the past two seasons, they have not lost since being beaten by rivals Manchester United three years and three days ago.

"It's a good competition," Guardiola said. "We are already in the quarter-final so we will see the draw. You cannot win four titles in one season when you don't play games seriously.

"For the players who haven't played it's good for them to find their rhythm and for myself to see them, that they are fit and they are good."

Though Southampton suffered another defeat just days after Friday's thrashing, Ralph Hasenhuttl was happy to see his players show a response as they finished the better of the two sides.

"It's a defeat but also a reaction," he said. "After a very, very difficult night on Friday, to come here and play against one of the strongest sides on this planet, you can think about easier challenges.

"It was important we showed a reaction for this game and we had this. That was the main goal for this game."

Things get no easier for Southampton, however, and they are due back at the Etihad for a Premier League meeting on Saturday afternoon.

"We will have a lot of very interesting video to watch from this game," Hasenhuttl said. "But we know they have a few players to come back so the side will not be weaker.

"Let's have a look. We want to be as nasty an opponent as we can be."