Auckland suffered a third straight 50-over loss while leaders Northern Districts also had their wings clipped in Hamilton yesterday.
With two rounds remaining, the Ford Trophy is fascinatingly poised.
ND and Canterbury are joint top and can feel good about their chances of being in the four-way playoffs.
But it's not so comfortable for Auckland, who remain on 12 points - having got just two points from their last four games - with Wellington now equal and Central Districts and Otago just two back.
Otago rattled up 332 for six in Invercargill, the highest one-day score on Queen's Park.
The foundation was laid by a 165-run opening stand by Hamish Rutherford (108) and Aaron Redmond (87), an Otago 50-over record.
Jesse Ryder belted 78 in 45 balls.
Rain interfered, leaving Auckland with an adjusted target of 279 in 39 overs. They were always battling, only Donovan Grobbelaar making an impact with a brisk 54.
The teams meet again at Eden Park on Sunday. Auckland need a form reversal, and sharpish.
In Hamilton, captain Daniel Flynn's unbeaten 122 underpinned ND's 215 for eight.
Wellington spinners Luke Woodcock and Jeetan Patel combined for five for 33 in 20 overs.
Wellington won by three wickets with 16 balls to spare.
In a game reduced by rain to 30 overs, Canterbury eased past CD by 64 runs in New Plymouth.
On Sunday, ND host Canterbury in a top of the table clash, while Wellington play CD in the capital.
Points: ND and Canterbury 18, Auckland and Wellington 12, CD and Otago 10.