Facing their first demotion from the top flight, Hamburg were nervous against Greuther Furth on Thursday at the Imtech Arena.
The second division outfit started the game well and had a number of chances to open the scoring, with Niko Giesselmann wasting the best opportunity of the game early in the second half.
Hamburg eventually took control of proceedings but failed to breach Wolfgang Hesl's goal, and Van der Vaart hopes they can prove more clinical in the return match.
"They started very well and we came into the game late, but we were better in the second half," the Netherlands midfielder said. "We still have a good chance of winning and we know we need to improve for Sunday.
"We're staying positive, though.
"A club as great as this belongs in the Bundesliga."
Hamburg will need to end an 11-game winless run away from home in all competitions at the Trolli Arena if they are to preserve their top-flight status.
