A sellout 4,500 crowd packed into Stanley Park to see Lightning claim a seventh win in 10 Blast games.
They reached their target of 180 with 10 balls remaining, returning to the North Group’s summit after successive defeats in the competition.
Croft hit four fours and two sixes in 44 balls and shared a third-wicket partnership of 114 with skipper Dane Vilas, who made 55 off 30, having come together at 31-2.
Nottinghamshire’s 179-7 included Samit Patel’s 45 off 36 balls and captain Dan Christian’s unbeaten 30 off 14, which included leg-side sixes off the last two balls of the innings from Danny Lamb.
Spinners Tom Hartley and Luke Wells stood out with two for 27 and one for 20 from their four-over spells as the Lightning (15 points) leapfrogged Northamptonshire at the top with four to play.
The Outlaws were put into bat and lost Alex Hales and Joe Clarke in the third and fourth overs.
Tom Bailey had Hales caught at deep midwicket for 22, having hit two sixes earlier in the over. Clarke then miscued Gleeson to mid-on.
Ben Duckett shared 46 in six overs with Patel before being dismissed when well set on 29, wicketkeeper Vilas taking the catch as the ball rebounded off his body.
Left-arm spinner Hartley was the bowler, and he also had Patel caught sweeping to deep midwicket and Tom Moores run out in the same over.
Steven Mullaney was lbw to the leg-spin of Wells but Christian and Calvin Harrison (17) gave the Outlaws a late boost, sharing an unbroken 47.
Lancashire opener Keaton Jennings scored 24 from 13 balls but he and Josh Bohannon were both caught off Luke Fletcher and Dane Paterson.
The weather hasn't always been kind to Lancashire at Blackpool, and certainly wasn't on their last visit over four years ago, but Croft and Vilas made hay in the Sunday sunshine.
Croft made the early running, pulling and sweeping sixes off Paterson’s seam and Patel’s left-arm spin, before Vilas overtook him and reached a 24-ball 50.
Vilas also hit two leg-side sixes as Lancashire careered towards a double over Notts.
Croft followed him to a half-century off 34 before Paterson and Patel removed Vilas and Tim David, caught at backward point.
Wells hit the winning runs, with Croft punching the air in delight. Croft said: “We got the win against one of the better teams in the division and it puts us in a great position.
“It was a brilliant win for the team and, on a personal note, it was very pleasing to come back here, play a T20 and do well. It was great to see so many familiar faces.
"It was the perfect day. It felt like we had it under control all the way.”
Lancashire are back in Blackpool on Thursday evening (5.30) to face Durham in the same competition.