The Americas Zone was the unique zone within Group 3 of the regional Davis Cup competition in 2018. The zone's competition was held in round robin format in Escazú, Costa Rica, from 28 May to 2 June 2018. The two winning nations won promotion to Group II, Americas Zone, for 2019.
Format: Round-robin basis. The winner of Pool A will play-off against the runner-up of Pool B and the winner of Pool B will play-off against the runner-up of Pool A to determine which two nations will advance to Americas Zone Group II in 2019.
Standings are determined by: 1. number of wins; 2. number of matches; 3. in two-team ties, head-to-head records; 4. in three-team ties, (a) percentage of sets won (head-to-head records if two teams remain tied), then (b) percentage of games won (head-to-head records if two teams remain tied), then (c) Davis Cup rankings.