Counties Manukau produced a barnstorming second-half display to beat defending champions Canterbury 33-21 in Pukekohe and seal a Mitre 10 Cup Premiership play-off spot.
Not since back in 1998 had the Steelers beaten Canterbury, but they scored five tries in a rousing performance under pressure on Saturday to take the bonus point and prolong their season.
Tasman will deny Auckland the final play-off place if they avoid defeat against Southland in Nelson on Sunday after Canterbury, who end the regular season at the top of the table, slumped to only their second loss of the campaign.
Toni Pulu scored the first of his two tries to give the Steelers a 7-6 advantage at half-time and they touched down four times after the break despite losing Sione Fifita to the sin bin, as well as Piers Francis and Jimmy Tupou to injury.
Pulu, Cardiff Vaega and Richard Judd went over in the space of 10 second-half minutes after Pauliasi Manu had scored shortly after the restart, with Daniel Lienert-Brown and Nathan Earle scoring the only tries for the champions.
Bay of Plenty can look forward to featuring in the Championship play-offs after clinging on for a 26-24 victory over Hawke's Bay in Napier.
Te Aihe Toma, Lalakai Foketi, Solomona Sakalia dotted down and there was also a penalty try for Bay of Plenty, who were dominant at the set-piece but were up against it in the closing stages as they edged it at McLean Park.
Waikato's hopes of making the play-offs were over by the time they snatched a 28-24 win at Wellington courtesy of Stephen Donald's last-gasp try - a result which meant the hosts finished second in the Championship behind Otago.