Pernille Harder's hat-trick handed Bayern Munich a winning start to their Women's Champions League campaign, beating Arsenal 5-2 in Group C. 

Harder, who scored 24 times in 48 appearances for Arsenal's London rivals Chelsea, once again haunted the Gunners, striking her first goals in the competition in almost two years.

After three games in the Women’s Super League, Arsenal sit sixth, having won once and drawn twice, with the latest defeat piling more pressure on head coach Jonas Eidevall. 

The Gunners started brightly at the FC Bayern Campus and took the lead in the 30th minute when Katie McCabe's delivery was swept home by Mariona Caldentey. 

However, the hosts drew level two minutes before the break when Georgia Stanway's searching ball picked out the head of captain Glodis Viggosdottir, who towered over her marker to loop the ball beyond Manuela Zinsberger. 

Bayern then took the lead in the 56th minute as a fast break saw Sydney Lohmann finish at the near post, only for Eidevall's side to respond nine minutes later when McCabe's corner was headed home by Laia Codina. 

But the German champions found themselves back in front soon after with a corner routine of their own, with Harder netting her first of the encounter with a header from Carolin Simon's cross. 

The Dane then notched her second with another well-taken header, before sealing her treble with an effort from close range, despite the best efforts of Zinsberger. 

Harder recorded a staggering 1.59 expected goals (xG) tally to Bayern's 1.89 total, as Arsenal were left to rue wasted opportunities, with six of their nine shots on target, but unable to trouble Maria Grohs for the most part. 

Elsewhere in the other early kick-off, Hammarby recorded a historic 2-0 victory over Austrian side St. Polten at the Tele2 Arena for their first triumph in the group stage of the competition. 

Vilde Hasund handed the hosts an early lead in the 18th minute with a brilliantly taken finish, striking the ball low into the bottom corner following Ellen Wangerheim's lay-off. 

The victory was sealed two minutes from time by substitute Cathinka Tandberg, who took a touch and placed the ball beyond Carina Schluter to put Hammarby top of Group D ahead of Manchester City's star-studded clash with Barcelona.