The win lifted the Swabians out of the bottom three with five games of the season remaining, but Stevens warned there was still a long way to go before they were safe.
"These three points are very important in our situation, but this victory was just one small step in our current situation," said the Dutch coach, who thanked goalkeeper Sven Ulreich for some important saves when the game was finely poised at 1-0.
"There's no time for celebrations," Ulreich told Sky. "It's a step in the right direction, but we have five finals to come."
Freiburg also have five matches to secure their Bundesliga status, with just two points now separating them from the bottom three.
If they succeed in beating the drop, it would be a major achievement, according to coach Christian Streich.
"Avoiding relegation would mean more to us than finishing fifth last season," he said.