Notts Unity Casuals skipper Rahim Karim was the only batsman to convert a good start into a big score, and this proved the difference against Belvoir.
Having been put in at the toss, Belvoir were pegged back by Tariq Mahmoud (3 for 35) in a suffocating spell of seam bowling.
Lewis Dann (34) and Jake Fisher (27) both looked to have mastered the conditions with a series of boundaries, but Shahzad Ahmed struck twice in consecutive overs, leaving the hosts 89-6.
James Clayfield and captain Ryan Lewis (34) dug in for another mini-recovery until the former was unluckily run out by an alert Ibby Asif.
Lewis bludgeoned the score past 150, but despite dogged resistance from Phil Irvine, the Casuals wrapped up the innings at 157.
Joe Bottomley punched a couple of holes in the reply in an aggressive opening spell of 2 for 26.
But this brought Karim who got his eye in and let loose with a string of powerful boundaries, while opener Nadeem Ghani held up his end with a more restrained knock of 32.
The two were separated at 72 when Danny Gibson castled Ghani.
Arslan Shah also took time the find his rhythm, but Karim (59 not out) was in full flow, and they embarked on an unbroken fourth-wicket stand of 86 in 82 balls to seal a seven-wicket win.