Son Heung-Min scored the only goal of Saturday's game 18 minutes into the first half to earn Leverkusen all three points in a contest that ended with both sides reduced to 10 men.
Defender Emir Spahic was sent off for the visitors, before Sokratis Papastathopoulos was dismissed in injury time for Dortmund following a second bookable offence.
The win leaves Hyypia's men four points behind Bundesliga leaders Bayern Munich, and the Finn was quick to hail the importance of the victory.
"I am especially pleased for the team," Hyypia said. "In the first-half, we really showed what's possible.
"After the break, we fought hard and we won, the victory was important because Dortmund were only three points behind us (before the match)."
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