The Outlaws, who lost the toss, won for the sixth time after reducing the hosts to 13 for three to move level on points with fourth-placed Lancashire on 12 points from 12.
Lancashire are only ahead on net run-rate with two North Division matches left after failing to defend 137 for four on a slow pitch, including a pair of 51s for Karl Brown and Steven Croft.
This was their fourth home defeat in six this season, having never lost more than twice at this venue in a Twenty20 campaign.
Former Lancashire all-rounder Steven Mullaney excelled in returning one for 14 from four overs of canny medium pace on a slow pitch before Notts made hard work of the chase.
They lost three wickets for 19 to slip from 63 for one in the eleventh over and ended up needing 13 off the last against Kyle Jarvis. Captain James Taylor hit successive boundaries off the last two balls with six needed to finish 33 not out off 21 balls.
Early wickets for Samit Patel, Harry Gurney and a run out hurt the hosts as Ashwell Prince chipped to mid-off, Paul Horton chopped on and Alex Davies was run out without facing a ball going for two.
But Brown ensured the Outlaws did not have things all their own way as he hit all of six boundaries accrued in a six-over score of 36 for three.
In fact, the in-form right-hander scored all of Lancashire’s first eight boundaries on the way to a 39-ball fifty, his third in a row, as he helped them reach 69 for three after eleven.
Unfortunately for the hosts, Brown holed out to long-on in the next off the medium pace of his childhood best mate Mullaney as the score slipped to 70 for four and ended a 57-run partnership with Croft.
They went without a four or six from the fifth ball of the eleventh over to the third ball of the 17th, although Croft and James Faulkner shared 67 unbroken for the fifth wicket to carry their side to something to bowl at
Notts lost Michael Lumb to a Jarvis slower ball in the third over of their chase and only reached six overs at 28 for one.
At halfway, they were 61 for one, needing 77 more with Alex Hales (30) and Riki Wessels together. But they lost three for 19 inside three overs to put the game back in the balance at 82 for four in the 14th.
Wessels cut Jordan Clark to point, ending a 47-run stand with Hales, who then miscued Stephen Parry’s left-arm spin to mid-wicket, before Patel cut Clark to point.
The target went to 45 off the last five overs and 21 off 11 balls when James Faulkner yorked compatriot Dan Christian and had Mullaney brilliantly caught at deep mid-wicket by a running Arron Lilley - 117 for six in the 19th. Chris Read also fell in the last over.