The home side had led 2-0 before Inter came back to win 3-2 with a 90th-minute winner.
Maran believes that his side should have kept more possession and thinks that Rodrigo Palacio's introduction was the defining moment for the away team.
"It's such a shame about this comeback, perhaps we should have kept the ball better," Maran told reporters.
"We always tried to score the third goal. We had a few great opportunities and tried to kill the game off, but unfortunately we were unable to take those chances.
"Palacio's introduction was decisive, as he caused us real problems. I don't think it is a deserved defeat."
The win takes Inter above Lazio into fourth place in Serie A.