However, big-match experience from players with a host of Tall Blacks, Breakers and NBL caps saw the Auckland team emerge 47-41 victors.
With a starting line like Casey Frank, Lindsay Tait, Duane Bailey, Aaron Nowell and Hayden Allen, Choppers showed how quick they could make the turnarounds - specifically with long court passes, as they have a familiarity the Juniors could not hope to match.
However, the young players hung in there and with a deep lineup were able to make whole shift changes, so their tempo never really went down, whereas Choppers would drift in and out.
Leading 11-7 at quartertime, Choppers went on a signature scoring burst with Tyler Kerlin's steal and layup moving them to 18-7 ahead.
While they missed a few shots, the Juniors' Toby Gillooly, Kaeleb Tyner-Wenman and giant 16-year-old Callum McRae - who even stood a nearly foot taller than Casey - were able to close the gap, as Quinn Clinton's three made it 21-18 at halftime.
Josh Aitcheson had a strong third quarter, highlighted by a good bucket despite a hard hit from Tait, while Choppers became frustrated with the referee calls against them.
Clinton took the Juniors into the lead with free throws, although there was a bit of confusion around the scoreboard at the threequarter hooter, with the Juniors up 32-31.
That was expanded to 36-31 and the Choppers looked to be in trouble, but they merely put all their first-stringers back on and ratcheted up into fifth gear.
Bailey hit a massive three-pointer to give his team the lead back 38-36, while Choppers kept the youngsters away from their hoop long enough to regather momentum - Tait scoring off good leadup work from Nowell.
Franks and Allen then got in on the act and at 45-36 with the clock ticking down, they were safe to cruise the match out.
Hawke's Bay's Rack City, the 2012 champions and previous runners-up, also made a statement as they three-point bombed their way to a 71-56 win over the Kaia International team on Saturday afternoon.
Kaia had the names - Japan's Jun Iwasa, Nigeria's Deola D'Brown Folarin and locals like talented young man Akira Marsters and HoopNation's organiser Paul Berridge.
But when Rack City's Karl Noyer coolly potted nothing-but-net from the three-point line on three straight occasions, the story of the match was setting in as Rack City took a 23-14 lead into the first break.
Folarin found Arthur Trousdale all over him, then he and Iwasa would try to up the tempo, but Rack City had the court pre-sighted like a machine gunner as they kept nailing the big shots, along with Marco Alexander and Bronson Beri getting a couple of nice layups for 33-24 at halftime.
Marsters tried to inject some spark in the third quarter, but Rack City expanded their advantage and played smart percentages, which told in the 51-39 scoreline coming into the final period.
Alexander also got into the three-point shooting spree in the final quarter, landing back-to-back buckets, and while Folarin had enough time for a steal and awesome one-handed jam, the game was long gone.
Today's Premier semfinals will be at 12 noon, with the final at 3pm.
Preceding that will be the women's and men's A Finals, starting at 1pm.