St Just will meet St Austell in the final of Cornwall's 50/50 Cup after beating Truro on Saturday.
Batting first, St Just were all out for 207 in 47.3 overs, with Dave Roberts' 85 the top score.
Truro's reply fell just 17 runs short as they were bowled out for 190, with Barry Purchase scoring 70, while Robert Clackworthy took 3-34.
St Austell, who had already qualified for the final, beat Grampound Road by 45 runs.
St Austell scored 202-7 in their 50 overs, before restricting Grampound Road to 157-8.
In the weekend's other games, Penzance beat Falmouth by two wickets, whilst Newquay overcame Werrington by one wicket.