The Norwegian star held off Eva Pinkelnig by 2.1 points on the Slovenian slopes, picking up a valuable haul of 254.8 points to now sit just 26 behind overall leader Chiara Hoelzl.
And Austria's Hoelzl struggled in Ljubno, languishing down in seventh place following disappointing jumps of 91m and 86.5m.
Pinkelnig – who is third in the overall standings – beat home favourite Nika Kriznar to the second spot on the podium, as the Slovenian jumper finished with a total of 250 points, 2.7 behind the Austrian.
Pinkelnig's compatriot Marita Kramer came fourth while Japan's Sara Takanashi finished fifth, but it was all about Lundby as her thrilling performance – her fourth victory of the season – left Hoelzl fretting at the summit of the table.
"A fantastic moment because I've had some difficult weekends," Lundby said.
"I'm happy, my shape is growing up and I had a better in-run position on a tricky hill like Ljubno."
Hoelzl was victorious in the team event on Sunday, however, as Austria soared to the summit of the podium with a points haul of 1008.7 – 3.6 ahead of second-placed Slovenia.
The overall World Cup leader was joined by Pinkelnig, Kramer and Daniela Iraschko-Stolz, as a final round jump of 92m from Pinkelnig helped seal Austria's hegemony.
And the Austrian team currently sit an imposing 2,001 points clear of Norway - who finished third - in the overall table, while Japan - who came ninth - occupy the third-place spot.
The women's ski jumping World Cup next heads to Oslo, where Hoelzl will be planning to get back to winning ways in the individual event following her disappointment in Slovenia.