The 29-year-old scored twice at the Esprit Arena as the Lions won the Rhine derby 4-1 on Saturday.
"It was a difficult match, but we finally kept our cool in front of goal and that was important," he told Bundesliga.com. "We weren't at our best, but in the end it's all about taking the three points.
"We've had a number of games this season where we played well but left empty-handed. We were all very relieved because there was pressure on us after losing the previous two matches.
"Our aim is to secure third place, but for that we still have to work hard. There was also some added emotion because it was a derby game, and Dusseldorf matched us really well for parts of the game."
Bayer are currently third in the Bundesliga with 48 points from 27 matches.