After a lacklustre efficiency, Dortmund seemed to be heading for a 1-1 draw earlier than Sebastien Haller headed on their first nook of the second half and Reyna stabbed it in on the far put up.
The guests, who’ve conceded eight targets of their final three league matches, shortly fell behind when unmarked Lee Jae-sung headed in a nook on the close to put up within the second minute.
New Dortmund signing Julian Ryerson levelled two minutes later with a closely deflected shot from exterior the field however there was little else to return from Dortmund in assault.
They did have a number of efforts on purpose by Karim Adeyemi within the second half however by no means actually threatened and ended up surviving some late stress from Mainz, who had their greatest likelihood when Anton Stach‘s low drive flew simply large within the 88th.
Reyna then stepped as much as give his group three factors and raise Dortmund, who face Chelsea within the Champions League Spherical of 16 subsequent month, as much as third on 31 factors, 5 off leaders Bayern Munich.