Stefan Ortega described his Manchester City debut as “perfect” after keeping a clean sheet in the goalless Champions League draw away to Borussia Dortmund which sealed top spot in Group G.

The 29-year-old goalkeeper stepped in to give regular stopper Ederson a rest, making his first appearance since joining from Arminia Bielefeld on a free transfer this summer.

“First Champions League game and my first official game for Manchester City,” Ortega said. “In Germany, my hometown and on this great stage with a clean sheet, so quite a perfect day for me.

“It was a nice stage for me and I am happy about the clean sheet and about the game.”

Ortega revealed he was only told by manager Pep Guardiola he would be making the start earlier in the day – a decision which caught him by surprise.

“I am happy that the manager said to me, ‘OK, are you ready?’” he said. “I was amazed, of course. Yesterday when I was on the pitch, I was told to be ready. Today in the team meeting Pep said, ‘Stefan, you start’. I was excited, yes.”

City snapped up Ortega in July after allowing United States international Zack Steffen to join Middlesbrough on loan.

Up until that point he had spent his entire career in Germany, having two spells at Arminia either side of three seasons at 1860 Munich.

But Ortega said he and his family have adapted quickly to life in Manchester off the pitch – with the bigger adjustments coming on it, playing in City’s high-possession system in which the goalkeeper is asked to play a key role.

“It is very different from my former team,” he said. “In my former team, I had a lot of shots and a lot of saves but here I only had three or four saves and in the second half nothing, so I had to be concentrating the whole game. This is the biggest difference.”

While Ortega was delighted with the clean sheet, it was a different feeling for Argentina forward Julian Alvarez, who was disappointed they drew a blank at the other end as he made only his fourth start since arriving from River Plate, playing the full 90 minutes.

“I’m very happy for having been involved in the game,” he said. “We are not pleased with the draw, but we are happy for having achieved the goal of finishing at the top of the group. We have had a consistent group stage overall…

“Manchester City is one of the best clubs in the world. I came here because I want to keep learning and growing as a player. I have learnt a lot since I arrived here.

“Training and playing with the best players in the world make you improve and become a better player. I’m going to always give my best to help the team.”

The impact Alvarez has made – four goals in 15 appearances mostly from the bench – has been overshadowed somewhat by the incredible scoring feats of fellow summer arrival Erling Haaland, but he is happy to keep learning from his fellow 22-year-old.

“We all know the sort of player Erling Haaland is,” Alvarez said. “He is very physical, he has amazing quality, with great movements, he is very quick inside the box and he is an outstanding goal scorer.

“He is a great player and a great person too. I have been looking at him a lot in training and I always try to learn from him. I keep learning things every day, not only from Erling but from the rest of my team-mates.”