The Volts picked up two points from the incomplete match to finish the round-robin stage of the competition third on 17 points - one point ahead of the Knights, who beat second-placed Auckland by two wickets at Mt Maunganui yesterday.
A home playoff in the one-day competition brings relief for the Volts, after the side finished dead last in the twenty20 competition and is stuck at the bottom of the ladder in the Plunket Shield.
If the Volts beat the Knights on Saturday, they will play the loser of the Auckland v Central Stags playoff match on Wednesday for a spot in next Sunday's final.
Otago Volts coach Dimitri Mascarenhas said the rain aided his side ''a bit'', but he was now focused on preparing for the elimination final against the Knights.
''We are very pleased. We knew we had some work to do to get there. It's good to be through to the elimination final and we are going to have a real tough game against Northern Districts, who we have had some tough games against this year,'' he said.
''They're a tough team. They fight hard, so it's going to be a real tough game. We will have to play at 110% to beat them.''
After starting the competition ''brilliantly'' - winning three of their first four games - the Volts have lost momentum, with just one win in their last four completed games, and have also had a couple of games rained off.
''This tournament we started brilliantly, but we haven't finished the group stage brilliantly. But the finals are a different kettle of fish,'' he said.
''The best teams always turn up for the finals, so hopefully we can be one of them.''
While logistics have not yet been finalised, the Volts will likely head straight to Queenstown to prepare for the match against the Knights, Mascarenhas said.
''The best preparation will be to go straight to Queenstown. So hopefully we can get that sorted and get down there and prepare well.
''The boys like playing in Queenstown. We know the conditions, we perform pretty well down there, so I think that's another positive for us,'' he said.
The match is in Queenstown because the Sparks are playing the Wellington Blaze in the women's twenty20 final at the University Oval on Saturday.
Had Auckland beaten the Knights, Canterbury would also have snuck into the playoffs with the two points gifted by the rain.
However, the Knights pulled off the upset and the rain denied the Cantabrians the chance to beat the Volts and advance to the sudden-death stage of the competition.
Rain only allowed 23 overs of play yesterday, enough time for the Volts to reach 109 for one after Canterbury captain Peter Fulton sent them into bat.
Hamish Rutherford was dismissed for just two, but opener Sam Wells reached 42 and captain Aaron Redmond struck 54 from 60 balls.
Otago beat the Knights by five wickets in their last match at Mt Maunganui on January 4, and by a whopping 222 runs in Alexandra on December 27 last year.
In yesterday's other match, the Wellington Firebirds beat the Central Stags by 22 runs in Wellington.
The Otago under-17 side was on the wrong side of a nine wicket hammering by Wellington at Lincoln yesterday.
Otago managed just 106 runs batting first, before Wellington knocked off the required runs in just 19.4 overs.
The Otago under-19 side had an almost identical loss to Wellington, also losing by nine wickets after scoring just 123 runs batting first.
Wellington chased the dismal total down in just 20.3 overs.
by Robert van Royen
