The home team were dismissed for 29 after 15 overs, no player reaching double figures.
In response, Nettleham posted 32-2 within six overs.
Adam Waters took a wicket, William File adding a run out.
The Sunday Firsts beat Barkston and Syston by three wickets.
Richard Hickling (4-26), William Broughton (3-25), Tom Johnson (2-25) took wickets as Barkston ended on 97-9.
Horncastle reached 100 for the loss of seven wickets, Jonathan Clark (32), Nathan Whiting (15 not oiut), Lewis Lovegrove (14) and Liam Wilkinson (12) aiding the victory.
On Saturday the Firsts host Alford Seconds (2pm), the Sunday side away at Reepham a day later (1.30pm).