The NSW Waratahs are facing a huge Super Rugby test against the unbeaten, new- look Melbourne Rebels after being stung in a 38-28 loss to the Jaguares.
The Jaguares offered the perfect response to their critics by scoring four unanswered tries in the opening quarter - including the first try within 17 seconds - before home fans at Velez Sarsfield in Buenos Aires on Sunday (AEDT).
Stung by criticism from former Argentine great Hugo Porta that they were a team with no soul, the Jaguares recorded their first win in four matches, ending their worst start since joining the competition in 2016.
It means the Waratahs, with one, last-gasp, win over the Stormers, a draw against the Sharks and now a loss, are already nine points adrift of Australian conference leaders the Rebels, who they meet in Sydney next Sunday afternoon.
The Jaguares were in scintillating attacking form from the start and winger Emiliano Boffelli had two tries on the board inside 11 minutes, the first from the kickoff, as they carved out a 33-7 halftime lead.
Fullback Joaquin Tuculet cut through the Waratahs' defence for their third after 16 minutes and flyhalf Nicolas Sanchez touched down again four minutes later to round off a fine team attack.
The Australians finally pierced the home defence after 35 minutes when number eight Jed Holloway picked up from a ruck and scored under the posts.
The Waratahs looked to reduce the deficit before the interval but wing Bautista Delguy intercepted flyhalf Bernard Foley's pass and raced away for the Jaguares' fifth try, with Sanchez kicking his fourth conversion.
The Waratahs emerged from the break intent on taking the game to the hosts and scored their second try in the 47th minute when Jake Gordon gave Curtis Rona a high pass over the defence and the wing went over with Foley converting.
The Jaguares got their sixth try with Tuculet feeding centre Matias Orlando wide on the left after a series of scrums close to the Waratahs line.
The visitors finished with a flourish with two more tries either side of the hooter from replacement Nick Palmer and fullback Israel Folau, who chased a kick from deep in the Waratahs half and beat Tuculet to touch down.
Foley then took his tally to four conversions.