The Cherries were undone by an early Mike Grella goal at Gigg Lane as their poor end-of-season form continued.
Groves said: "The first 15 minutes cost us. There wasn't enough energy and there wasn't a realisation that they'd come off the back of a good win and would want to start quickly. That cost us and cost us dearly.
"For large parts of the game we were in the ascendancy and we were the ones trying to win the game but the first 15 minutes really cost us. It's extremely disappointing.
"Before you come into a game like this, you speak about your mental approach and professionalism.
"Maybe we will look back at the game and see some positives but at the moment, there aren't any. That's why it's difficult to speak in front of people because you're so disappointed and that's a mild way of putting it."
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