The Dutchman was understandably pleased with his side's performance, having clung onto a significant scalp in the Ruhr derby, but did not expect a below-par showing from the hosts
The Royal Blues took a commanding two-goal lead into the second half, and despite Robert Lewandowski's best efforts to pull one back for the title holders, they held on for the victory at Signal Iduna Park, putting them five points clear of their local rivals.
Speaking after the match, the former Hamburg and Red Bull Salzburg coach revealed he was expecting a better performance from BVB, but nonetheless was delighted to take the maximum reward for their efforts back to Gelsenkirchen.
"We were a little surprised that Dortmund played differently from their usual style, but we adjusted well to keep it at 2-1," Stevens said.
"After all, we fought a great battle and brought home a well-earned victory."