Aubameyang gave Dortmund a lead which lasted only four minutes before Eric-Maxim Choupo-Moting brought Mainz level. Lewandowski then scored from the spot after Elkin Soto was sent off, and the Polish striker became the Bundesliga's top goalscorer with his 11th of the season with the last kick of the game.
Mainz on top
Dortmund had Lukasz Piszczek back in their starting XI for the first time in 189 days, slightly relieving their defensive problems and bringing experience to a side which had the highest average age (26.8) of any Dortmund team since March 2009. That average has been increased by Manuel Friedrich, who came up against his former side and was given a few early situations to deal with as Mainz started brightly.
Roman Weidenfeller could not keep hold of Zdenek Pospech's shot, preferring instead just to push the ball back out into play before turning a second effort from Johannes Geis behind for a corner. Mainz were showing no sign of nerves and dominating play, particularly in midfield, prompting Klopp to make an early change by introducing Nuri Sahin, initially left on the bench for the first time since 11 September, for Sven Bender.
Little really changed in terms of the balance of play with a confident Mainz continuing to take the game to their guests. They almost took the lead shortly before the break when Dortmund's defence struggled to deal with a corner and Stefan Bell was allowed room to glance Geis' cross onto the top of the crossbar. Anything he could do, Aubameyang could do too, albeit from a greater distance with a 25-yard volley touched onto top of the bar by Loris Karius.
After a largely uninspiring first 45 minutes Klopp, perhaps unsurprisingly, exhausted all of his options by bringing Henrikh Mkhitaryan and Sebastian Kehl on for Marco Reus and Jakub Blaszczykowski at the start of the second half, yet the first chance still fell Mainz's way with Choupo-Moting flashing a shot wide of the far post.
Okazaki spurned the next opportunity for the hosts, volleying over from a tight angle, and the profligacy was to haunt Mainz as they fell behind from an unstoppable free-kick, placed in the top left-hand corner by Aubameyang. It was a moment of class followed by a moment of madness by Piszczek, who reached out his arm to block Yunus Malli's route in the penalty area, and the referee pointed to the spot.
Choupo-Moting stepped up to sweep the ball past Weidenfeller, Dortmund's advantage lasting just four minutes. A further four minutes passed before the visitors regained the lead from a penalty of their own. Soto reverted to last-ditch measures to keep Lewandowski's shot out with his hand, earning a red card and allowing the Pole to put BVB back in front, a lead they extended with a second penalty, which Lewandowski also converted.
Line-ups and statistics