Colin de Grandhomme was promoted up the order to continue Auckland's momentum and did just that, hitting Neil Wagner for six off his second ball. De Grandhomme went deep once more before Otago found an effective if illegal way of putting a halt to his big hitting. An apologetic James McMillan lost control of a full ball and sent a beamer into de Grandhomme's elbow, forcing him to leave the field on 15.
Mahmood didn't let de Grandhomme's departure halt the progress of Auckland's innings, finishing with 79 from 49 balls as he guided the Aces to an imposing 187-2.
In reply, the Volts made the strange move of opening with strike bowler Wagner and leaving Brendon McCullum in the sheds. The promotion didn't pay off, however, with Wagner falling for four in the second over.
McCullum and Aaron Redmond were keeping near the required run rate of nine in the seventh over when it all began to fall apart. McCullum's dismissal for 26 triggered a top order collapse which saw Otago lost four wickets for five runs, leaving the Volts teetering at 56-5 and Auckland firmly in charge.
From there, only one team was likely to win it and Auckland made no mistake, restricting Otago to 157-8, despite a resolute 56-run partnership between Dimitri Mascarenhas and Nathan McCullum.
Spinner Ronnie Hira was the standout bowler for the Aces, claiming 3-17 from his four overs, including the consecutive wickets of Jimmy Neesham and Redmond to turn the tide in Auckland's favour.
Elsewhere, Canterbury stayed on Auckland coat tails with a commanding 61-win over a listless Wellington at the Basin Reserve.
Canterbury got off to a flying start and looked set to threaten 190 when openers George Worker (45) and Rob Nicol (16) began their innings at pace. Peter Fulton (44) kept the momentum ticking over but, when Worker departed after he skied a catch from the bowling of Jeetan Patel, Canterbury's innings lost its mojo.
From 84-2 as Worker left the field, they staggered to 151-8 from their 20 overs, as Patel (3-18) and Andy McKay (3-19) kept Wellington in the match.
In reply, Wellington's chase never got off the ground as Matt Henry claimed the scalps of Rory Hamilton-Brown and Michael Pollard early on.
Only James Franklin cracked double figures, and his 33 was never going to be enough to get Wellington over the line as Nicol turned the screws with his off-spinners.
The all-rounder claimed a match-best 4-21 from four overs as Wellington's woeful run chase ended at 90.