A Conor Devlin brace wasn't enough for the home side in the see-sawing affair, as four goals in a frantic second-half saw Uni suffer their first home defeat this season in a 3-2 loss to Rockingham City.
It was a tentative start at The Mac with Patrick Morrison's one-on-one chance at the 15-minute mark from an Andrew Xydas lofted ball highlighting the opening stages.
The stalemate continued with both sides defences holding firmly with a short break in play as Rockingham player Christian Hogge received treatment after a collision with Josh Marocchi at the half hour mark.
A late chance crafted by Luke Randazzo in the middle of the park opened up space down the right for Lloyd Prout, with the winger's eventual ball finding Morrison whose shot narrowly missed the mark.
Rockingham ended the uneventful half on top dictating possession and Oriol Fernandez rewarded the visitors by walking through the defence and slotting into the bottom right corner with 37 minutes played.
City came out of the sheds with intent, as their forward pressure forced Uni into a number of errors in midfield, but Janssen's men fought tirelessly to work their way back into the match.
Devlin came to the rescue at the 61st-minute mark with a piece of individual brilliance. The combative midfielder weaved his way around the edge of the box and his left-footed curled effort beat keeper Alf Brincat at the far post.
UWA then hit the lead just minutes later with Devlin dispatching home from the spot after Morrison was awarded a penalty following a challenge by Brincat.
Rockingham responded swiftly, with Drew Clarke's shot from distance smashed home from point blank by Hogge after Alex Preece's initial save.
The second half roller coaster continued, with City hitting the lead again after Marocchi was judged to have fouled in the area. James Harmer belted the ball home sending Preece the wrong way with just over 20 minutes remaining.
It remained 3-2 as Rockingham claimed the first away win at The Mac all season, with UWA condemned to their second consecutive defeat.
It was a frustrating day for the club, with the 18's suffering a heavy defeat and the reserves experiencing a 3-0 loss.
UWA travel to Joondalup City next week as they look to get their season back on track.
It was a contrasting day for the women's sides, as the Div 1 First Team ensured they sit top of the league table after a resounding 4-0 win over Wanneroo thanks to a brace each to Safyr Iriks and Amelia Bates.