See main article: 2018 Davis Cup.
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.
Date: 28 May–2 June
Location: Costa Rica Country Club, Escazú, Costa Rica (hard)
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.
| Pot | Nation | Rank1 | Seed |
|---|---|---|---|
| 1 | 81 | 1 | |
| 84 | 2 | ||
| 2 | 94 | 3 | |
| 95 | 4 | ||
| 3 | 99 | 5 | |
| 104 | 6 | ||
| 4 | 110 | 7 | |
| 113 | 8 | ||
| 130 | 9 | ||
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.
| Placing | A Team | Score | B Team |
|---|---|---|---|
| Promotional | 0–2 | ||
| Promotional | 1–2 | ||
| 5th–6th | 2–0 | ||
| 7th–8th | 2–1 | ||
| 9th | colspan=2 |
and were promoted to Group II in 2019.