By FOX Sports staff
Dortmund's bid to win the league crown for a third successive year looks all but over after they fell to an embarassing loss at the Signal Iduna Park, despite taking the lead after 17 minutes through Robert Lewandowski.
Hamburg responded a minute later Artjoms Rudnevs before going ahead four minutes before the half-hour mark when Son Heung-min netted with a powerful effort, and things went from bad to worse for the hosts five minutes later when Lewandowski received his marching orders for a challenge on Per Ciljan Skjelbred.
Although the visitors too were reduced to ten men in the 59th minute when Jeffrey Bruma was handed a red for a professional foul on Marco Reus, they went on to seal all three points as Rudnevs and Son both picked up their second of the game.
Admitting HSV were deserving winners in the end, Sahin admitted his side paid for a sloppy start, even though it had been them who took the lead.
"We didn't play well in the opening stages and struggled to get into the game," he said on the club's official website.
"We were punished for it by conceding two goals and had to play from behind, which wasn't easy with 10 men. But you also need to say that in the end it was a deserved win for HSV.
"The defeat hurts - you just cannot concede four goals at home."
With a UEFA Champions League Round of 16 clash with Shakhtar Donetsk coming up in midweek, the Turkey international admits Dortmund cannot afford a repeat of Saturday's display if they are to keep alive their dreams of European glory.
"We need to be highly focused because Donetsk will also punish our mistakes," Sahin added. "So we need to show an improved performance.
"Wednesday is a different game - one we want to win."
Sahin is currently at the Signal Iduna Park on loan from Real Madrid, who signed him from the German giants in the summer of 2011.