Derick Hougaard’s first try in Tigers colours, a first score of the season for Matt Smith and Johne Murphy’s seventh of the campaign set up the victory at Welford Road.
Mauger described it as a hard-fought win, and added that the performance reflected the belief within the team.
The Tigers centre said: “I thought that the boys showed a great attitude out there. Physically we kept them out, apart from the late try, and the attitude was awesome. It felt good.
“We knew we had to build on our performance against Bath. We knew we had to be playing well to be beating the top sides like Harlequins. There’s good belief in the team and I think that was reflected in the way we played.
“They are a top-four side and we knew it was going to be hard, so it was good to get the four points."
Tigers are now preparing to play Sale in the Guinness Premiership on Friday night, and Mauger has called for a repeat of the attitude for the trip to Edgeley Park.
“It’s always a tough game up there,” said Mauger. “We need to go up there and display a lot of attitude, like we did against Harlequins, and try to nullify their strengths and play to our own.”