Koeman knows Everton can do "much better" and expects his new-look side to become a more cohesive unit as the season progresses, pointing to the string of big-name players out through injury.
"We had a lot of control, certainly in the first half". They are tasked with the giant responsibility of replacing Romelu Lukaku. You need to defend well but with that you need a good goalkeeper.
He said: "The end of the transfer window is more realistic to speak about targets and what is possible". I think that all bodes well for the games we have ahead of us. I don't say impossible but 25 goals is a lot and we need to find other ways.
"But in hard moments in the game he showed his experience".
"We are disappointed about the result clearly because we wanted to get off to a winning start if we could but the key from our point of view, it was the level of performance we are looking to produce so I was reasonably pleased with that", he told Sky Sports.
The glow from Rooney's 199th Premier League goal was nearly erased when Fletcher went close to equalising after half-time with a stinging strike.
"It's probably going to be a day too late (for Everton game)".
But Koeman reflected on the top sides' far superior attack forces, saying: "Compare that to the big teams and what they have on the bench - or even in the stands - it is a big difference to Everton".
Only this summer, Wayne Rooney has returned to the Goodison Park, and former Barcelona forward Sandro Ramirez from Malaga also.
Rooney had already played one home game - a Europa League qualifier against Ruzomberok - in his second spell as an Evertonian following his close-season move from Manchester United.
However, the efforts of Ronald Koeman and his team should also be applauded for not only have they brought one of the brightest Spanish talents to the English shores, they have done it quickly and at a price which could prove him to be steal of the transfer market one year from now.