Melbourne Victory suffered a 2-1 loss to Werribee City in the NPL2 West at Epping Stadium on Sunday.
After Nuh Sehavdic gave Victory an early lead, goals from Jay Kelly and Hiro Nagatomi saw Werribee claim three points.
The host had the better of the second half, but it was punished late on as Werribee struck against the run of play.
Victory opened the scoring in the eighth minute.
Birkan Kirdar, 16, produced a brilliant run through the middle before playing in Sehavdic, who finished clinically into the bottom corner.
In what was an even opening half, Werribee equalised in the 31st minute.
Kelly was released with a long pass down the left before beating Victory goalkeeper Matthew Sutton in a one-on-one.
A goal-line clearance from Victory centre-back Benjamin Carrigan kept the host level heading into half-time.
Victory looked the more likely throughout the second half, although a recovering Sutton made a great save to deny Kelly before Kirdar hit the post on the hour-mark.
As the host pushed, Werribee found a late winner as Nagatomi finished from an angle after Victory gave up possession deep in defence.
Head coach Gareth Naven
"I think we're a team of two contrasts. I think there's a team out there that's really working hard and understanding what we need to do in regards to how to compete in the NPL2 competition and then I think there's a team out there at times where we look like boys. I think that's the difference.
"We conceded a really late goal where we looked like a group of boys out there. I think what we need to do is, if our team is looking to progress, we need to understand what the opposition is trying to do and we need to get better at what we need to do in defence, attack and transition.
"Also, the perception of effort in regards to what they think they need to do is slightly different to mine so that needs to get closer, especially in today's match. In previous matches, they've definitely looked like a team who can handle the competition, but today I don't think we achieved that."
Victory's under-20s made it four straight wins with an 8-2 thrashing of Werribee City.
NPL2 West 2018 Round 9
Melbourne Victory 1 (Nuh Sehavdic 8')
Werribee City 2 (Jay Kelly 31', Hiro Nagatomi 87')
Melbourne Victory: Matthew Sutton; Andrew Visciglio, Benjamin Carrigan (c), Maker Maker, Aaron Anderson (Luke Goulding); Thierry Iradukunda, Nicholas Hatzigeorgiou; Jack Palazzolo (Nicholas Sette (Brandon Lauton)), Birkan Kirdar, Yazid Said; Nuh Sehavdic.
Victory makes the trip to Eastern Lions in Round 10 on Saturday, April 28.