Pinner struggled against a good home bowling attack in their match at Hawridge and Cholesbury on Sunday.
Only John Spencer (31), Asif Khan (22) and Mark Amadee (34) were at ease at the wicket, and the visitors' total of 134 for nine never looked like it would be enough to win the game.
An exceptional innings of 114 not out, which included 86 in boundaries, from Sri Lankan batsman Gunnesekarar, dominated the Hawridge reply and proved to be the difference between the two sides.
No other batsman made double figures as the target was made for the loss of four wickets.
Pinner begin their Middlesex Championship campaign this Saturday when they are at home to