Kiessling's header had initially gone wide, but then finished up in the net courtesy of a hole in the netting, and was awarded as a goal by referee Felix Brych.
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Hoffenheim nearly replied straight away as Modeste got the better of Leno, poking the ball under him and into the net before incorrectly being adjudged offside.
The hosts had even more reason to be frustrated with the officials when Kiessling's missed header on 70 minutes spun back into the net through a gap in the side netting.
Referee Brych evened things up slightly when he gave Hoffenheim a soft-looking penalty, which Roberto Firmino saw saved by Leno, before his rebound bounced off a defender, both posts and out.
Schipplock turned the ball in at the far post following an 88th-minute scramble, giving Hoffenheim brief hope of a point, which they may well have come away with had it not been for Kiessling's bizarre 'goal'.