The Foals had started the season in poor form, but ended Armin Veh's troops six-match unbeaten run in the Bundesliga on Sunday, with the Dutchman on target
Having qualified for the Champions League last season, Lucien Favre's side have so far failed to live up to expectations this term, registering a string of disappointing results.
However, they overcame newly promoted Frankfurt, with the Dutchman finding the net, and De Jong admitted that his side were in dire need of a win.
"It's a good feeling. We're pleased that he won today," he told Bundesliga.com. "Leading 2-0 at half-time gave us a lot of confidence.
"It wasn't an easy game, but we were compact and hardly let them have any good chances to score, and we grabbed two ourselves.
"We needed this win. It was important. Our last few games didn't go as planned so this win will give the whole team confidence again."
De Jong was also on the score sheet as Gladbach crashed to a 4-2 loss to Fenerbahce on Thursday, but insisted that personal achievements only matter if the team does well.
"it's always nice to score, but it's worthless if I score and we lost the game. But I'm a striker, so of course I'm pleased when the ball hits the net."
The former Twente man was left out of Louis van Gaal's Netherlands squad this month, and despite admitting his disappointment at losing his Oranje place, he has vowed to keep fighting.
"Of course I'm a bit disappointed. Everybody wants to play for their national team, but now I'm focusing on the Under-21s. I'm looking forward to it.
"I'm still at an age where I can play for them and we have an important play-off against Slovakia and we want to qualify for the European Championship."