The win came at the right time because Otago had lost its Air New Zealand Cup game to Hawkes Bay on Friday night and the Otago Spirit women's team was beaten by Hawkes Bay 21-3 in Dunedin on Saturday.
Otago won the national B competition in 2006 and has made a sparkling start to its 2008 campaign.
A penalty try late in the half gave Otago B a 10-0 lead at the break after a disjointed first spell.
The Otago forwards tightened their game in the second spell and provided cleaner ball for the backline.
Cave led the attack in the second spell, using his speed to beat two defenders with a sparkling run down the touchline for a try.
The outstanding player for Otago was prop Dane Maraki, who was strong in the scrum and with the pick-and-go. No 8 Cam Goodhue had the strength to break the advantage line.
Andrew Parata had a strong defensive game at centre and was able to break the line, while Casey Stone turned in a good defensive game at fullback and was lively on the counter-attack.
