The Blues kept alive their title defence with a last-gasp 20-19 victory over the Chiefs and the Brumbies beat the Hurricanes 35-28 to complete the Super Rugby Pacific semifinal line-up on Saturday.
The Chiefs lost the top seeding they earned by topping the regular-season standings to the Crusaders, who outmuscled the Reds 32-12 on Friday, but still progressed to the last four as "lucky losers".
The 12-time champion Crusaders will host the Blues on Friday in Christchurch, where they are unbeaten in 30 Super Rugby playoff matches, while the Chiefs will stay in Hamilton to play the Brumbies on Saturday.
The Chiefs looked to have locked up victory at Waikato Stadium on Saturday when a try from centre Daniel Rona and 14 points from the boot of Damian McKenzie gave them a 19-13 lead with time running out.
The Blues have been playing catch-up since losing their first two matches of the year, however, and they battered away at the Chiefs defence after the hooter until lock Josh Beehre reached over the line to score and Beauden Barrett converted.
"There's been a whole lot of ups and downs through our season and... although there's another week for us, we've got to enjoy that kind of moment," said Blues skipper Patrick Tuipulotu.
The Chiefs, runners up for the last two years, were left stunned after leading for most of the game and will need to regroup over the next week before they resume their bid for a first title since 2013.
"I thought we had that game in the bag," said lock Tupou Vaa'i. "I guess footy's a strange game sometimes, you can start on a high and then it can humble you real quick."
The final playoff would have been a dead rubber had the Chiefs won, with both teams guaranteed a spot in the semifinals under the "lucky loser" rule, but Beehre's try ensured a heated contest on a chilly night in Canberra.
HURRICANES STRIKE EARLY
The Hurricanes initially grabbed the momentum with crisp backline moves resulting in tries for fullback Ruben Love and winger Fatafehi Fineanganofo in the opening quarter.
The Brumbies hit back in more prosaic fashion with hooker Billy Pollard going over twice and prop Allan Alaalatoa once, all from close range, to give the hosts a 21-14 halftime lead.
The home side showed they also had some flair soon after the break when an inside pass from Rob Valetini set fullback Tom Wright free to carve through the defensive line for a fourth try.
The Hurricanes, though, responded in kind when winger Bailyn Sullivan ran a beautiful line to cut the deficit to 28-21 with 55 minutes on the clock.
The Brumbies went back to battering down the front door for their fifth try from James Slipper but his fellow prop Pasilio Tosi powered over 14 minutes from time to make it a one-score game again.
The Hurricanes pressed for another try to send the tie into overtime but the Brumbies managed field position well and held firm to keep the Australian flag flying in the competition.
"It felt good to earn ourselves another week, we knew it was probably going to take everything we had," said Brumbies skipper Alaalatoa.
Hurricanes co-captain Du'Plessis Kirifi was disappointed but said his team should take some pride in finishing the season strongly after a stuttering start.
"We just weren't good enough tonight and they were," he said.