Wagner celebrated the third anniversary of his appointment at Huddersfield with a long-awaited victory, their first of the season and his 50th as boss, thanks to a 29th-minute own goal from Timothy Fosu-Mensah.
That ended a run of 658 minutes without a home Premier League goal for Huddersfield, who were replaced at the bottom of the table by Fulham as they moved up to 18th.
Wagner told Sky Sports: "I don't care who scored it or how we performed. People know we can perform better. The pressure was on for both teams but how we fought - we left everything on the grass.
"It was deserved. First half we were clear and second half we were able to keep them away from our goal.
"This is huge for us. We have the winning feeling back. For sure it is one of the most important wins we've had in the last three years. Everybody needed this belief back. It's massive for us.
"Nothing is more important than this winning feeling, happy faces in the dressing room and in the club and we are back in the race after 11 games."
A fifth straight league defeat will naturally increase the already considerable pressure on Fulham boss Slavisa Jokanovic, who remains confident in his ability to guide the Cottagers to safety in the remaining 27 games.
"I trust in myself. People know I've been here for two years and how I work," Jokanovic told Sky Sports.
"The process has not started well. There are many games ahead of us. We must improve ourselves.
"I am thinking about my team and myself. Definitely we are not at the best level and are looking for improvement."