The Cod Army squandered a commanding two-goal cushion after Danny Andrew’s sixth goal of the season and Callum Morton’s second-half penalty at Highbury.
A first win in four would have seen the hosts climb out of the dreaded League One drop zone.
But Grayson’s charges crumbled as Leam Richardson's side hit back and an impressive 10-minute burst saw Callum Lang, Will Keane and Curtis Tilt complete a fine comeback win.
Grayson said: “We have to deal with pressure better when we’re under it because you’re going to be under pressure against the top teams.
“Against Wycombe on Saturday we were under pressure for 10 minutes and conceded two goals in that time.
“We’ve got to make sure we deal with it better. We need to be more ruthless, streetwise and sense danger, even if it means being solid and riding the storm then we have to do that.
“That comes with managing games and a bit of experience that maybe we haven’t got.
“They got a bit of momentum and we caved in as such. Keeping the ball was important at that stage and we didn’t do that because we kept giving it away cheaply. That allowed them to keep asking questions of us.”
Grayson’s side have shipped six goals in their last two games and have only one clean sheet to their name all season.
The manner of the goals on Tuesday night left Grayson and the head coach knows he needs to find a way to tighten his team up.
“I’m really frustrated and disappointed because we’ve given ourselves a great opportunity to win a game,” added Grayson.
“We were go 2-0 up against a team that are in the top three. We played really well up until that point, passed the ball well and did all the jobs we wanted the players to do."
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