Unicol were proving dogged opponents and, when Cambridge keeper Fraser Nicholls pulled down one of their attackers in the box, Hall stepped up to equalise from the spot and leave the game level at the break.
Cambridge had by far the best of the second half but struggled to break Unicol down, raining in the shots for no reward as the visitors held firm.
Just as the students looked to have played a compelling and telling part in the title race, Carmichael's dramatic finish gave the WaiBOP Premiership its final twist of the season.
Cambridge now look forward to a tough home and away play-off against Waitemata, winners of the AFF/NFF Conference, with the victors securing a place in the 2016 Northern Regional Football League.
For their part, second-placed Ngongotaha did all they could.
They won impressively 4-1 at Otumoetai on Saturday, with the goals coming from Mitch Miller, Luke Barker, Josh O'Sullivan and Yamil Casas.
But, ever since they dropped points at the Matamata Domain, at the start of August they were relying on a Cambridge slip-up which never came to give them a shot at the title.
Unicol rebounded from what, for them, would have been a heart breaking loss with a 4-2 win over lowly Katikati on Sunday in the second game of their weekend double-header.
In the other premiership games, a Mark Glenister hat-trick helped third-placed Melville United to a 4-2 win over Rotorua United.
David Brennan grabbed Melville's fourth, while Steffano Riley and Ash Gower-Rudman replied for Rotorua.
Tauranga Old Blues cemented fourth spot with a 1-0 win at Matamata Swifts.
- Points:
Premiership: Cambridge 58, Ngongotaha 51, Melville 39, Tauranga Old Blues 37, Papamoa 29, Otumoetai 25, Waikato Unicol 25, Matamata 23, Rotorua United 22, Katikati 16, Tauranga Boys' College 14, Tauranga City 11.
Championship: Claudelands 44, Kawerau 43, West Hamilton 43, Te Puke 33, Cambridge 32, Tokoroa 24, Matamata 23, Te Awamutu 17, Whakatane Town 14, Tauranga Old Blues 13, Ngongotaha 7.
Results
WaiBOP Football results at the weekend:
Premiership:
Otumoetai 1 Ngongotaha 4
Melville 4 Rotorua United 2
Cambridge 3 Waikato Unicol 2
Matamata 0 Tauranga Old Blues 1
Waikato Unicol 4 Katikati 2 (Sunday).
Championship:
Cambridge 1 Kawerau 0
Matamata 0 W Hamilton 1
Claudelands 5 Whakatane Town 2
Te Puke 3 Ngongotaha 0