The HSV defender rose to head in a last-minute goal which made it 1-1 and denied Freiburg all three points – which they would arguably have deserved for their performance in northern Germany.
Instead, Admir Mehmedi’s goal did not prove enough for Christian Streich’s men, who will go into the final two games of the season with their destiny potentially taken out of their own hands, depending on other results this weekend.
That Hamburg were still behind heading into the last minute would have come as a surprise considering the way they started the game.
With confidence oozing, they could have raced in front with Pierre-Michel Lasogga denied by Roman Burki early on.
Felix Klaus should have given Freiburg the lead, though, but he failed to bury their first chance of the match.
His effort nevertheless led to a turn in the tide and Freiburg took the lead midway through the first half when Mehmedi drilled in a powerful shot under the crossbar after Burki’s punt forward was helped on by Karim Guede.
The Swiss forward came close to adding a second goal just after the break – but Rene Adler made two fine saves to deny him.
Adler then made saves from Klaus and Vladimir Darida as Freiburg maintained a level of superiority which was to last until the very last throw of the dice for Hamburg.
Rafael van der Vaart’s corner was not cleared and Ivica Olic’s header was only pushed into the air by Burki, who was second to the loose ball as Kacar put his head in and sent the ball over the line, much to the delight of a sell-out crowd.
Freiburg almost snatched victory in the final seconds of five minutes of stoppage time, but Adler kept Jonathan Schmid’s stinging free-kick out to earn what could be a crucial point for Hamburg, who remain a point ahead of their opponents.