Grimes, who was one of Melbourne’s best, said the team was pleased with the way it started, but simply fell away after the main change.
“In the first half, we did everything we spoke about and it felt like we were further ahead than what the scoreboard showed,” Grimes told melbournefc.com.au.
“They got a couple of cheap goals and we really felt up and about. We were giving them no time and we were moving the ball well.
“After half-time, it was a completely different intensity and the boys dropped off and we ran out of legs.”
He said Hawthorn’s increased work-rate, combined with Melbourne’s drop in pressure proved costly.
“We played at a really good intensity in the first half and we took it easier in the second half,” Grimes said.
“They kicked a couple of quick goals early and then our heads and spirits dropped, as we went back into our shells. Our momentum dropped - there was no real reason or excuse for it.
“They just wanted to work harder in the second half and we dropped off.”
“If you blew the siren at half-time, we’d obviously be really happy with the game, but we know you can’t just do that,” he said.
“We’ll review the tapes and see the things we did well in the first half and the things we didn’t in the second half - it will really stand out.
“But it also gives us some confidence to know that we can start well like that against a team like Hawthorn and put them under pressure.”
Despite the loss, Grimes said the team is eager to make its mark against Sydney Swans at the MCG in round one.
“When you lose games like we did against Hawthorn and you know you’ve won it at half-time, it makes you keen for the following match,” he said.
“You really want to play four quarters and we’ll learn a big lesson from this match.
“The next time we start well in round one, there will be a bigger focus of the second half against Sydney.”