It was a classic slugfest, but Auckland did enough in torrential rain to hold out Wellington 21-15 at Eden Park on Saturday.
The hosts scored two tries to nil, secured back-to-back wins and moved into the top four with their fifth victory in this year's ITM Cup, while last year's beaten finalists slipped to consecutive defeats after a shock loss to Manawatu last week.
Wellington made much of the game's attacking play but were unable to tame the difficult conditions and breach a stoic Auckland defence, with fly-half Lima Sopoaga's five penalties not enough for victory.
The home side were able to score two first half tries, including one with the last act of the first half, which proved the difference in a tight game.
In suffering their first loss to Auckland in four games, the Lions also relinquished the Fred Lucas Cup, in honour of the 1923-30 Auckland All Black.
Sopoaga and his Auckland counterpart Matt Berquist were both unsuccessful with early penalty shots on goal.
The home side then put the first points on the scoreboard through their first try to lock Liaki Moli, who stretched out in the tackle to plant the ball over the line for a 7-0 lead after 10 minutes.
The Lions opened their account with a penalty to Sopoaga, answered by a second one to Berquist and Auckland led 10-3 after the opening quarter.
A concerted passage of play by Wellington was almost rewarded with a try when lock Jeremy Thrush surged through a hole and up into Auckland's 22. Instead they were handed a penalty from the next play and Sopoaga kicked it from in front.
Auckland attacked with vigour close to Wellington's line and Berquist managed to dart through to score their second try, which he failed to convert from out wide on the stroke of halftime as Auckland went under the stand holding a 15-6 lead.
A broken field injection by left wing Alapati Leuia followed by a separate run by centre Charlie Ngatai gave the Lions early second-half momentum. Another promising raid was followed by another penalty in front of the uprights and Sopoaga obliged to close the deficit to 15-9.
The Lions remained patient against tight close quarter defence and were rewarded with another Sopoaga penalty that closed the gap up to three points, but Berquist banged one over himself straight away and Auckland now led 18-12 on the 60-minute mark.
Sopoaga kicked his fifth penalty, but Auckland once more pulled six points clear almost immediately with another Berquist penalty in reply.
Another Berquist penalty hit the uprights as the time remaining wound down to inside the final 10 minutes and Wellington rallied for field position and a converted try to win the match.
They finished the game at the right end of the park inside Auckland's half and with a midfield scrum. But once more the home side kept them out and they held on for the win.
Tries: Moli, Berquist
Pens: Berquist 3
Pens: Sopoaga 5
Auckland: 15 Brent Ward, 14 Atieli Pakalani, 13 Winston Stanley, 12 Jamie Helleur, 11 Bryce Heem, 10 Matt Berquist, 9 Toby Morland, 8 Chris Lowrey, 7 Daniel Braid (c), 6 Adam Kleeberger, 5 Andrew van der Heijden, 4 Liaki Moli, 3 Charlie Faumuina, 2 Ash Dixon, 1 Tevita Mailau.
Replacements: 16 Tom McCartney, 17 Angus Ta'avao, 18 Kurtis Haiu, 19 Peter Saili, 20 Auvasa Faleali'i, 21 Gareth Anscombe, 22 Dave Thomas.
Wellington: 15 Apoua Stewart, 14 Julian Savea, 13 Shaun Treeby, 12 Charlie Ngatai, 11 Hosea Gear, 10 Lima Sopoaga, 9 Alby Mathewson, 8 Rodney So'oialo (c), 7 Scott Fuglistaller, 6 Faifili Levave, 5 Api Naikatini, 4 Jeremy Thrush, 3 Neemia Tialata, 2 Dane Coles, 1 John Schwalger.
Replacements: 16 Ged Robinson, 17 Jacob Ellison, 18 Nick Passi, 19 Dean Brunsdon, 20 Ruki Tipuna, 21 Fa'atonu Fili, 22 Tajhon Mailata.
Referee: Chris Pollock