Mats Hummels was hugely disappointed as Borussia Dortmund were held to a 2-2 draw against newly-promoted Darmstadt in Sunday's Bundesliga clash.
Aytac Sulu's 90th-minute equaliser secured the visitors a point after a double from Pierre-Emerick Aubameyang had overhauled Marcel Heller's opener.
Successive draws against Hoffenheim and Darmstadt leave Dortmund four points adrift of Bundesliga leaders Bayern Munich, ahead of a trip to the Allianz Arena next weekend.
And Hummels insisted that the visitors were fortunate to leave Signal Iduna Park with a point.
"It was a game that you normally win. Darmstadt had an awful lot of luck and earned a point with two shots at goal," Hummels told reporters.
"It happens. It must be very clearly said that they relied on pure luck, but we must deal with it.
"We have recently suffered two extremely unnecessary point losses - especially today. I cannot put it into words.
"Darmstadt were dead, they no longer believed in themselves and we gave them a chance to score."
The centre-back was critical of his side's defending as Darmstadt opened the scoring with with a counter-attacking move finished off by Heller in the 17th minute.
"The opponent scored with an unmarked volley from 13 metres. We had five, six players 20 metres from the goal - that's no defence," Hummels added.
