Fink took the captain's armband of Heiko Westermann and gave it to the Dutchman after a run of three consecutive defeats, and a 2-1 win in Mainz was the result, taking the northern German side back to within a point of the top six.
"As a coach, you have got to know people well and I think I am good at that," said Fink.
"I felt that Heiko needed this change He wants to be able to do his job in peace and quiet and you could see on Saturday that he was able to focus on his own performance more."
Van der Vaart will wear the captain's armband again for Saturday's clash with Fortuna Dusseldorf, although the other 10 players on the field will not necessarily be the same as they were a week ago.
"Even if we won our last game, that doesn't mean I have decided who will play against Dusseldorf," Fink said on his club's website.
"I may make changes. My lads have got to be motivated every day of the week to play on Saturday."
Nevertheless, two-goal Heung-Min Son should lead the Hamburg attack on what Fink hopes will be a repeat of what he saw seven days ago.
"I expect my team to show the same discipline and presence as they did against Mainz," he said.
"Dusseldorf are no weaker so everybody is going to have to be prepared to give everything for each other - that is what I demand from my team.
"Only then will we improve and have lasting success."
Fortuna coach Norbert Meier believes his side are lacking just a bit of luck to have lasting success, which for them would mean a second straight season in the Bundesliga.
Meier's men have yet to occupy a place inside the bottom three, but with five games of the season to go, they are perilously close.
"A few things have gone against us in the second half of the season," he said.
"We lost in the last minute to Freiburg, we lost in the last minute to Bayern Munich."
They have lost four of their last seven games, only drawing the other three, and should Augsburg beat Borussia Monchengladbach tonight, only goal difference will be keeping them above the drop zone.