Lancashire set Somerset only 68 to win after losing the final two wickets of their second innings cheaply.
Somerset knocked off the runs with relative ease to leave Lancashire 56 points behind Essex with two games left.
Essex turned the screw when they thrashed Warwickshire by an innings and 56 runs on Thursday.
They are only the second county to win the title having been promoted the previous season since two divisions were introduced to English cricket in 2000.
(Reporting by Martyn Herman, editing by Pritha Sarkar)
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