The Merseyside club, 12th in the league, exited the FA Cup and League Cup in the semi-finals this season and Martinez felt his side lost their focus in the celebratory atmosphere at the King Power Stadium, where Leicester were crowned champions after the game.
"There is no such thing as winning the players back. We got caught up in the atmosphere and celebration," Martinez told reporters on Tuesday. "That lack of intensity cost us."
Martinez called for his squad to focus only on Wednesday's clash against Sunderland, when asked if he had received any assurances over his future from Everton bosses. Sunderland, fourth from bottom, can guarantee survival if they win.
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"It is a huge game, and not just for what Sunderland are playing for. From our point of view, we want a reaction to Leicester. The only thing that matters is to avoid any distraction," he said.
Defender Ramiro Funes Mori is back in the squad after completing his three-match suspension, while midfielder Gareth Barry has a good chance of being involved, Martinez said.
(Reporting by Shravanth Vijayakumar in Bengaluru; Editing by Mark Trevelyan)
