Goalkeeper Roman Weidenfeller spared Borussia Dortmund's blushes with a pair of shootout saves to help them progress to the third round of DFB-Pokal after a 1-1 draw with Union Berlin.

Weidenfeller expertly saved Union's first two penalties before Philipp Hosiner struck the crossbar to give Dortmund a 3-0 spot-kick triumph following a gruelling 120-minute encounter with their in-form second-tier opponents.

A first-half own goal by Michael Parensen looked set to be enough to see the hosts advance, before Steven Skrzybski scored a sensational equaliser for Union with 10 minutes of normal time to play and forced Weidenfeller to be the hero.

Thomas Tuchel handed starts to several fringe players as Pierre-Emerick Aubameyang, Christian Pulisic and Marc Bartra joined a lengthy injury list already containing the likes of Marco Reus and Andre Schurrle, and extra time is the last thing his depleted squad needed.

Union are second in 2.Bundesliga, having won six of their previous seven, and they matched last season's Pokal finalists for much of the contest.

The visitors could have taken a shock lead in the fourth minute through Kenny Price Redondo, who sprung the Dortmund offside trap, but opted to shoot and dragged wide when striker Collin Quaner was well placed in the box.

Adrian Ramos then shot straight at Union goalkeeper Daniel Mesenholer and Mario Gotze had his effort deflected over during a frantic opening 15 minutes.

Union, who looked every bit a side flying high in the second tier, forced Weidenfeller to palm away a fiercely driven cross and dive at the feet of Quaner as they continued to trouble their hosts.

After Gotze and Nuri Sahin forced saved from Mesenholder, the deadlock was eventually broken two minutes before the break when Union's Parensen inadvertently steered a cross from Dortmund debutant Bruun Larsen into his own net with his chest.

Emre Mor blazed over the top in the 50th minute, but Union substitute Hosiner's off-target snapshot demonstrated that the visitors continued to pose an attacking threat of their own.

They thought they had the equaliser after 69 minutes via a tap-in from Kristian Pedersen's header across goal, but Dane had drifted offside.

But Union did sensationally draw level in the 80th minute through substitute Skrzybski just moments after entering the field, as he connected on the volley from a half-cleared corner and powered the ball past a despairing Weidenfeller into the bottom corner.

Mor fired against the post in the dying stages, but the tie went to extra time.

Mesenholer produced a brilliant double save from a Matthias Ginter header and Ousmane Dembele's follow-up three minutes into the additional half hour.

Union missed a glorious chance to prevent the game going to penalties midway through the first extra pariod as Hosiner took advantage of a misjudged Weidenfeller clearance and rounded the keeper, before dithering on the ball and failing to convert into an open goal as Dortmund recovered and the game went to penalties.

Dembele, Ginter and Gotze all converted as Weidenfeller performed his heroics to deny Felix Kroos and Stephan Furstner, with Hosiner striking the woodwork as Dortmund survived a major scare.