North Harbour won their first game of the ITM Cup season in thrilling fashion, with an after-the-siren penalty seeing them edge Southland 26-25 on Sunday.

Daniel Halangahu's sixth goal of the night was a match-winner for the visitors, who overcame a 22-7 deficit in the first half to triumph in Invercargill.

Willis Halaholo crossed twice for Southland in the first half, but they were to lament a second-half comeback from North Harbour - former NSW Waratahs five-eighth Halangahu the hero with 11 points after the interval.

The revival from Steve Jackson's North Harbour was all the more impressive, given their last-start 43-0 loss to Wellington.

Bay of Plenty's tumultuous season continued in a 43-10 defeat to Waikato.

Backing up after a win over Southland on Wednesday, Bay of Plenty barely fired a shot as Waikato made it back-to-back victories.

Brad Weber crossed twice for the visitors in Tauranga, while Michael Mayhew, Zane Kapeli, Jordan Payne and James Tucker also touched down for Waikato.

Bay of Plenty have a 2-2 record in the Championship, while Waikato improved to 2-1 and moved their points differential into the positives.