Their main threat in the chasing pack is Auckland, who sit in second spot on the table and had an even first day's play against Otago.
Two wickets apiece to Lockie Ferguson, Tarun Nethula and the returning Colin Munro were counter-balanced by a consistent effort from the Otago batsmen, with five players making 30. Derek De Boorder's 50 and an unbeaten 46 from Sam Wells were the main contributors as Otago recovered from 97-4 to reach 266-7 at stumps.
Northern Districts and Wellington are the only other sides with a glimmer of hope of claiming the title, and ND took the upper hand when the two sides began their clash at Bay Oval.
Wellington won the toss and decided to bat, but came to rue that decision when ND ripped through them for 151.
Spinner Joe Walker took his maiden first-class five-wicket bag with 5-46, while Ish Sodhi chimed in with 2-49 as the spin duo bowled 53 of the innings' 83 overs. Debutant Brett Randell took two wickets, including the scalp of Luke Ronchi for a golden duck, and Corey Anderson sent down four overs as he ramps up his bowling workload.
Wellington were paced by Fraser Colson's patient 66 from 214 balls, and claimed the wicket of Henry Cooper to reduce ND to 11-1 at stumps.