Bayer Leverkusen
The match lived up to its billing and the result left Bayern and Leverkusen level on 10 points at the top of the standings.
The Spaniard who took over the then struggling club in October last year, led Leverkusen to a sixth place finish and a Europa League semi-final spot last season.
Xhaka joins Xabi Alonso's Leverkusen after spending seven seasons with Arsenal in which he made 297 appearances, with 23 goals and 29 assists, and helped the club win two FA Cups.
Roma youth product Bove stabbed in the winner on the rebound in the 63rd minute for his first European goal.
The 19-year-old Wirtz, in top form since his return this year following a months-long injury break, fired in to cancel out Union's lead through Victor Boniface in the 51st and leave the tie open ahead of next week's return leg in Belgium.
The last eight will be played in four German cities as part of the mini-tournament, with the final on Aug. 21 in Cologne.
Bundesliga leaders Borussia Dortmund are hoping captain Marco Reus will be fit for Sunday's match against in-form Bayer Leverkusen as they look to reignite their stalled title run.
Champions Bayern Munich survived some late pressure to win 3-1 and end Bayer Leverkusen's 12-game unbeaten league run
Champions Bayern Munich will kick off 2018 with an almost complete squad after top scorer Robert Lewandowski, Mats Hummels and Joshua Kimmich were declared fit.
Louis van Gaal has surprised everyone with what he said about Borussia Dortmund, and it was considered a lack of respect for the club.
Bayern Munich will face Bayer Leverkusen at the opening of the Bundesliga on Friday at 8:30 p.m.
