De Boer was "very happy" with the win that his side achieved in the Croatian capital and believes that they have given themselves a good chance of advancing.
"We have taken a big step in the right direction, although obviously we also want to be in the Champions League after winter," De Boer is quoted as saying on the official UEFA website.
"I am very happy as we dominated most of the time. They started pretty well and had two good chances to score at the beginning.
"After that we got a grip on the game and at certain points we had 66% of possession. We also created some chances in the first half but failed to take them. It was also important to not concede a goal."
The two sides meet again at the Amsterdam Arena in a fortnight.