Luciano Spalletti suggested he was unhappy at the complacency of Inter's performance as they defeated Frosinone 3-1 in Serie A on Sunday.
Inter closed on Champions League qualification with victory through goals from Radja Nainggolan, Ivan Perisic and Matias Vecino, yet they were pushed all the way by Frosinone in the second half before the clinching third strike.
Spalletti was delighted with a result that leaves third-placed Inter six points clear of Roma in fifth, but he was frustrated his side let Frosinone back into the game.
The head coach believes a more mature display would have had the game wrapped up long before Vecino found the net.
"It was a really difficult and important game at a key time," Spalletti said.
"We made life a bit harder for ourselves and gave Frosinone a chance when they had nothing to lose instead of killing the game off. We created our own problems, we needed to show the same maturity for the whole match.
"Our solidity at the back is a great advantage but the result should have been sealed sooner. We had lots of chances, including ones where we had men over and we needed to wrap things up."
Nainggolan similarly bemoaned the way Inter reacted to a contest they were controlling with ease.
"We thought it was a bit too easy," he told Sky Sport Italia. "But these games are difficult, especially when you relax.
"[Frosinone] work hard, are really aggressive and have a lot to lose, so they give everything. After it went to 2-1, we did well to hold on to the ball and add another goal to finish it."