The visitors pegged Attenborough back to 76-4 from the first 30 overs with all the bowlers keeping a tight rein.
Phil Irvine and Danny Gibson (2 for 37) knocked over the openers, helped by smart fielding from Sam Penford and Joe Bottomley.
Then captain Martin Shoemaker (111 not out), who had scored only 26 from his first 70 balls, was joined by keeper Jack Harrison and the runs started to flow.
The latter took three fours from consecutive balls, while the skipper plundered 22 off one over in a run-a-ball fifth-wicket stand of 62 before Bottomley castled the keeper.
Despite the best efforts of Andy Dann, Bottomley and Gibson, the hosts passed 200 when, at one stage, 150 had looked more likely.
In reply Belvoir captain Lewis Dann (25) and Tom Neville (22) provided a steady start, but the bowling was accurate with Charlie Simkiss (2 for 40) to the fore.
Wickets fell and the run rate grew, but Penford (19) and a particularly aggressive Irvine (30) steadied things with 42 for the sixth wicket.
Bottomley (26) carried on the good work, but the run rate continued to climb with Chris Tolley (2 for 41) and Martin Rayner (2 for 34) holding back the tide.
Even with 30 needed from 12 balls Bottomley and Gibson were still looking to win the game, but the former was bowled by Jandu (2 for 51), leaving the latter to block out the last over.