Centre Ace Malo replied for Wanganui but with 14 minutes left, Talanoa sealed the deal with his third try, with Wanganui reserve back Pehira Huwyler only getting a consolation five-pointer inside the final minute.
North Otago's defence was tenacious in the second stanza after the Darling try, with Wanganui's attack being far too one-dimensional and further hampered when captain Peter Rowe came off after being hit in the eye.
The weight of having to defend for up to 85 per cent of the first half also wore them down.
"We held them really well in the first 40 minutes, one mistake really blew it out to 15-3," said coach Karl Hoskin.
"The second half we just couldn't get into the game. Four little errors and they scored off all our errors.
"I think they had maybe one strike play, and the rest was off our mistakes."
North Otago's four tries earned them a crucial bonus point on a weekend where Mid Canterbury, Wairarapa Bush and West Coast have also confirmed their rise in 2013 by getting wins on the road.
The Top Four now have a five-point break on the best of the rest, which includes Buller and Wanganui.
It would take a miracle for the frontrunners to stumble in both their remaining matches while Wanganui would likewise have to gain maximum points for things to change.
"We'll just go weekend by weekend, game by game. We can't control where we end up now," Hoskin admitted.
In the search for how it all went so wrong, both Wanganui's scrum and suspect lineout are said to have held up well - Sonny Woodmass and Nick Cranston securing their own ball while slowing North Otago's momentum.
Out wide, Malo and winger Sailosi Naqiso did not get the opportunities they needed, while Rowe was formidable in the tight before his departure.
However, North Otago weren't lacking for inspiration either as their captain and blindside flanker Josh Clark was in superb form supplying his team plenty of ball - until a late knee injury which may end his season.
Lock Eric Duff was also the pick of tight five for the home team, while halfback Robbie Smith looked to have nearly scored a try but was unsighted by referee Mike Lash.
Under the pump for most of the first half, Wanganui opened the scoring in the ninth minute with a Zyon Hekenui penalty, but just six minutes later North Otago centre Lemi Masoe made a half break and fed first-five Ratu Vaituinaruku who grubber-kicked ahead.
Talanoa, under an injury cloud before kickoff, outpaced Wanganui's cover defence and from 5-3 they never gave up the advantage.
After a Ed Keohane penalty, the killer blows were either side of halftime.
Wanganui created a four-man overlap but it was Talanoa who ended up getting the try-scoring pass - 80m back up the field.
After the break, despite the blustery southwesterly, a series of phases from the forwards brought North Otago back into Wanganui's 22m - Smith feeding Darling to score.
Wanganui finally got into the opposition danger zone for first-five Areta Lama to put Malo over for a converted try to keep hope alive at 22-10.
But Talanoa had one more candle for his cake as he finished a play that swept 70m - Smith got the momentum rolling and after a chip kick on halfway, Vaituinaruku handed off for his winger to score in the corner.
North Otago then shut it down, with Huwyler's try coming too late to save the hopes of another Meads Cup finals appearance.
North Otago 27 (Chris Talanoa 3, Ralph Darling tries; Ed Keohane 2 con, pen) Wanganui 15 (Ace Malo, Pehira Huwyler tries; Zyon Hekenui con, pen). HT: 15-3.
