Harris, who was in the Lions team which reached the final in 2004, was recalled to the starting line-up for Saturday's encounter at The Den.
But Steve Morison missed a penalty as goals from David Murphy, Cameron Jerome and two from Matt Derbyshire secured a 4-1 win for the Premier League side before Danny Schofield's late consolation.
"We had plenty of chances but didn't take them," said Harris.
"They did take them and that was the difference. Matt Derbyshire is a quality finisher - I thought he was excellent."
Source: PA
Source: PA