The ACT Brumbies missed the chance to lock up the Australia conference when they crashed to a 30-16 Super 15 loss at home to the lowly Auckland Blues in Canberra on Saturday.
Jake White's Brumbies, chasing their first finals appearance since 2004, only needed one point to top the Australian table and clinch a playoff spot in the last regular round of the tournament.
But their loss was compounded later when defending champions Queensland Reds scored a bonus-point 32-16 win over the NSW Waratahs to claim the Australia conference with most wins during the season after both finished on 58 points.
The Brumbies were left to sweat on results in South Africa later Saturday to find out if they would make next weekend's playoffs.
The Blues put a wretched season behind them to secure only their fourth win in 16 games, with their All Blacks Keven Mealamu, Ma'a Nonu and Piri Weepu leading the way, outscoring the Brumbies three tries to one.
Auckland jumped out to a 14-0 lead after 17 minutes through converted tries by LiaKi Moli and Daniel Braid, and went on to lead 21-13 at half time before holding on comfortably in the rain.
The Brumbies were uncharacteristically poor in defence, one of their strong points this season, and missed a total of 34 tackles.
"We are gutted about that result," South African coach White said.
"The reality is that we let ourselves down tonight on our defence, which was something we have prided ourselves with all season.
"But all credit to the Blues, they were under the pump, their coach is under the pump and it's another lesson in rugby that you can never underestimate any opposition."
The Brumbies had most of the territory and possession amid rain squalls in the second half but could not convert it into points, with kicks from Zack Holmes and Jesse Mogg both going astray as the team sought a losing bonus point.
But poor option-taking and handling cost them the few scoring opportunities they had.
The loss also soured Brumbies' hooker Stephen Moore's 100th Super Rugby appearance.
"Although we haven't had the results we've stuck tight this season and it's good to finish this way and have a good couple of wins for our coach and for the franchise as well," Blues skipper Mealamu said.