Arsenal led through Mariona Caldentey's strike in Germany, but Bayern captain Glodis Viggosdottir brought the home side level before Sydney Lohmann put them ahead.

Laia Codina equalised for Arsenal midway through the second half only for Harder to find the net three times in the final 20 minutes to secure an impressive win for German champions Bayern.

Swedish side Hammarby won their first ever group stage game 2-0 against Austrian champions St Poelten, who are appearing in the group phase for the third season in a row.

Vilde Hasund's long-range effort gave Hammarby the lead and Cathinka Tandberg followed up her late winner in qualifying by wrapping up the points with another goal two minutes from time.