Somerset thrashed a woeful Notts by 325 runs to go top of the table and will be crowned champions if the Lord's match ends in a draw.
Somerset captain Chris Rogers scored his second century of the game in Taunton, before announcing his retirement from the sport, as they added 208 runs in 32 overs before declaring at lunch on 313-5.
Chasing an imposing target of 541 to win, Notts were bowled out for 215 to lose by 325 runs.
Rogers, a former Australia test opener, scored his hundred off 139 balls, adding to the 132 he posted on day one.
Somerset must now play a waiting game as they will be deprived of a maiden title if either Yorkshire or Middlesex triumph on Friday, with the promise of a thrilling finale in store.
Middlesex closed on 81-2 in their second innings, trailing Yorkshire's first-innings total of 390 by 39 runs.
Yorkshire are still in the box seat after Tim Bresnan's superb 142 not out propelled them to a 120-run first-innings lead, before Middlesex began slowly chipping away at their advantage in reply.
After Sam Robson and Nick Compton were swiftly removed to leave Middlesex on 2-2 after four overs, Nick Gubbins (39 not out) and Dawid Malan (37 not out) steadied the ship to guide them safely through to the close.
(Reporting by Toby Davis, editing by Pritha Sarkar)
