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The Volts need to win to guarantee a home venue for the semifinal on Wednesday and keep up their winning impetus, coach Mike Hesson said.
"It's about keeping that momentum, and going into the next game with the confidence to know that when we hit the semifinals we are playing our best," he said.
If Canterbury beats Northern Districts tomorrow and Otago loses, the semifinal will be in Christchurch rather than Dunedin.
"Obviously, that's not our preferred option because we'd like to be playing at home. But we're four points ahead going into the last round and are in control of our own destiny."
Otago will have to do without match-winner Brendon McCullum.
The hard-hitting wicketkeeper-batsman has been released to play for New South Wales in the Australian domestic twenty/20 competition and will miss the important fixture.
It is a loss, but Hesson believes it could be a blessing in disguise.
"We've only had Brendon for a couple of games, so it is not a huge difference. Obviously, we will welcome back Aaron [Redmond]. He's got some runs in the A tournament and is back and feeling confident."
It is the only change to the side which beat Central District by 63 runs on Wednesday.
McCullum would have been unavailable for the semifinal anyway, so it will give Redmond an opportunity to get an innings under his belt, Hesson said.
Last season, McCullum played just two matches for Otago but they turned out to be match-winning performances.
He scored an undefeated 108 to help Otago get past Canterbury in the semifinal, then smashed a remarkable 170 in the final against Auckland.
However, Otago has plenty of experience playing in big matches, having reached the past two finals and the semifinal in 2005-06.
"The guys look forward to it and know what they are going to be confronted with rather than being uncertain."
Otago has hit form at the right time, with a comprehensive 125-run win over Canterbury and a 63-run win over Central Districts in the past two weeks.
The skipper, Craig Cumming, has been in scintillating touch. He scored a magnificent century against Canterbury and is the leading scorer for Otago, with 329 runs at 65.80.
English import Dimitri Mascarenhas has enhanced his reputation as a consistent boundary hitter with some devastating innings.
Against Central he walloped a rapid half century. His ability to push the scoring rate and take advantage of the batting power plays has been of real benefit.
Ian Butler has been a surprise package with the ball, taking 11 wickets at 21.
He has also played some useful cameos with the bat.
And South African-born left-armer Neil Wagner has been a terrific signing. He is the competition's second-leading wicket-taker with 16 scalps at an average of 19.18.
Wellington is at the bottom of the competition table and out of contention. But with a large contingent of international-quality players in the squad, the Firebirds are a real threat.
English import Graham Napier leads the most value player rankings. He is the competition's leading wicket-taker with 18 wickets but is yet to really fire with the bat in the one-day tournament.
Dropped Black Caps pace bowler Mark Gillespie will have a point to prove, as will all-rounder James Franklin, who was dropped after the test series against the West Indies
Otago v Wellington
Otago: Craig Cumming (c), Aaron Redmond, Shaun Haig, Greg Todd, Neil Broom, Nathan McCullum, Dimitri Mascarenhas, Derek de Border, Warren McSkimming, Ian Butler, Neil Wagner, James McMillan.
Wellington: Matthew Bell (c), BJ Crook, Grant Elliott, James Franklin, Jeremy Dean, Chris Nevin, Graham Napier, Luke Woodcock, Jeetan Patel, Iain O'Brien, Mark Gillespie, Harry Boam.