MCC set off with gusto, Bosisto (21) and Overy (74) reaching 41 in just seven overs.
Bosisto was out to a fine catch by Warner, after which Overy batted with a mixture of caution and aggression in fruitful partnerships with Soames (16) and Rowe (39).
He finally fell with the score on 148, having hit 11 fours and a six.
Grady (34 no) and Beagles (15 no) pushed on in the latter stages to give MCC a total of 223-6.
Some sterling work behind the stumps by Belvoir’s own Ryan Lewis helped keep the score down.
In reply, the Duchess’s XI made a poor start, both openers falling cheaply.
Keast (40) and former England one-day international Dalrymple (26) staged a slow but steady recovery and an elegant Warner (40) upped the momentum with three sixes.
With the required run rate increasing, skipper Darren Bicknell was stumped going for the big shot.
Always behind the pace, the home team lost wickets steadily in the face of some fine bowling and finished on 152 all out, giving MCC a comfortable win by 71 runs.
The Imogen Skirving Memorial Trophy was presented to winning captain James Overy, who also picked up the Vic Heppenstall Spirit of Cricket Award for his 74.
The series, held to showcase the work of sports and education charity the Belvoir Cricket & Countryside Trust, is now tied at six games all.