Di Matteo replaced Jens Keller as Schalke's boss on October 7 and sat on the bench for the first time on Saturday as the North Rhine-Westphalia-based club triumphed 2-0 at home over Hertha Berlin.
It was just the third clean sheet Schalke have managed in all competitions this season.
The win took Schalke to eighth in the Bundesliga with Klaas-Jan Huntelaar and Julian Draxler scoring either side of half-time but Di Matteo was most impressed with his defence.
"It wasn't a necessarily spectacular game but it was important for us to get the three points," the former Chelsea manager told Schalke's website.
"A very positive thing is that we also kept a clean sheet. It was a great performance defensively.
"Hertha caused us a few problems, as we expected. We scored two goals and had even more chances, particularly in the opening stages.
"My team was well organised but we can improve our playing style. But that will come when our confidence grows after picking up a win or two."
Visitors Hertha just edged the possession and took more shots than Schalke (15-7) and Di Matteo claimed he wants his team to be more dominant as the season progresses.
"We have to try and have more possession in future and be more in tune so that we will create more chances. But we can't change everything at once," the former Italy international said.
"You could see that the team were unsettled at times but that's normal when the season hasn't started as you had hoped.
"Our focus is now on Sporting Lisbon. We want a good result in the [UEFA] Champions League."
Captain Benedikt Howedes added he was impressed how Schalke had performed considering Di Matteo had had so few training sessions with the full squad due to last week's international break.
"We wanted to keep things tight through the middle and keep the two defensive midfielders central. We weren't always able to do that but we tried to implement the manager's instructions and we didn't allow them many chances as a result," the defender said.
"It's not a huge one but we've taken a good and important step in the right direction.
"We have to carry on working patiently and keep progression step by step. Hopefully we can continue like this."
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