Bayern Munich Secure Slim Lead Against Manchester United in Champions League First Leg
Harder, raised as a fan of United, netted the opener within the opening two minutes by slipping behind the hosts defence.
"Netting twice at Old Trafford feels like a dream realised," the Danish forward remarked.
Marking their debut in a womens Champions League quarter final, United stood firm instead of crumbling under the initial setback.
Skipper Maya Le Tissier restored parity via a penalty kick following contact with the ball on Bayern defenders arm, that of Glodis Viggosdottir.
With a modest attendance at the Theatre of Dreams, the latter period gained momentum more gradually until a burst of three goals across 13 minutes towards the close.
Harder, who fetched a record breaking fee upon signing for Chelsea back in 2020, delivered yet another sharp strike after exploiting her speed to break clear.
This advantage held briefly before Hanna Lundkvist nodded home from Le Tissiers inswinging corner.
Yet Bayern clung to their edge when Momoko Tanikawa carved out room to drill into the distant corner with six minutes remaining.
"The positive aspect remains that this matchup stays open," noted Uniteds manager Marc Skinner.
"I feel annoyance over the goals we let in, as they seem quite avoidable, yet these can be swiftly addressed ahead of the return fixture, fully aware of their dangers."
The powerhouse from Germany anticipates progressing to the final four during the rematch set for next Wednesday.
That said, their route to a maiden European triumph appears challenging.
Barcelona seem poised to await in the semi stages, having crushed domestic foes Real Madrid 6-2 on the road in their opening quarter final clash.