"It is better to be on the pitch than on the bench, but the boys when they are playing did well, so if I'm on the pitch for 15 or 20 minutes, I do my best", he told BT Sport.
The closure of the English transfer window on August 9 means Chelsea now can not sign any players until January.
The Croatian global arrived at Stamford Bridge on a season-long loan deal towards the end of the summer transfer window but was forced to wait until the second game of the season to make his debut for Chelsea.
"We need to continue working for what we want, our process, today we had two midfielders one 19 and one 21 years old, we need to give them the confidence to play, but our way, our process, is to improve and give these chances to to the young players".
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Sarri said he started the match with Hazard on the bench because he still seemed exhausted after helping take Belgium to the World Cup semi-finals in July.
"For me there were many things positive in the first match against Manchester City".
"The transfer window in England is already closed". I feel good here.
On his first taste of the Premier League, Kovacic added: "Well, the tempo is higher, there is more space, but as I said it's not hard to adapt when you are surrounded by great players".
"It would be a bit odd that they would sell me now while they can't sign a replacement".
Chelsea FC's record signing made his debut in a 3-0 win over Huddersfield Town at John Smith's Stadium last weekend.