Otago had relinquished their top-four placing when North Harbour beat Bay of Plenty 41-8 on Friday night but Otago's bonus point win on Sunday ensured they remained just six points behind leaders Canterbury.
Auckland and Wellington are second and third respectively.
Fly-half Nick Evans was instrumental in Otago's win, scoring 16 points from a try, penalty and four conversions, before Callum Bruce came on and kicked a penalty and a conversion.
Otago rattled up five tries in all with Jason Macdonald, Matt Saunders, Craig Clare and Seilala Mapusua all touching down.
Northland's points came from a David Holwell penalty but they remain rooted to the foot of the table having failed to muster a win in six rounds.