Antarctic ice loss is expected to become a major driver of long-term sea-level rise, yet its regional impacts on vulnerable Pacific Island nations remain uncertain. Using the ISMIP6-2300 ensemble, we calculate Antarctic drainage-basin–resolved elastic sea-level fingerprints from ice-thickness changes simulated with and without ice-shelf collapse. Simulations including ice-shelf collapse substantially increase Antarctic contributions to global mean sea level by 2300 and strengthen the role of several East Antarctic sectors alongside West Antarctica, shifting the balance of dominant sources of mass loss. These changes amplify relative sea-level rise across the Pacific, with equatorial islands such as Kiribati and Tuvalu projected to experience more than 20 \% higher rise than the Antarctic-driven global mean by 2300. South-central islands, including French Polynesia and the Cook Islands, also exhibit enhanced amplification, whereas the Chatham Islands experience a smaller increase. Applying these Antarctic-driven relative sea-level shifts to historical tide-gauge extreme-value distributions shows that the return periods of historical 100-year extreme sea-level thresholds shorten progressively across Pacific Island sites, with ice-shelf collapse advancing the transition toward more frequent events. The magnitude and timing of exposure depend strongly on which Antarctic basins lose mass and whether ice-shelf collapse occurs. By linking Antarctic basin-scale mass loss to island-scale sea-level responses, this framework provides Antarctic-specific information for improving regional sea-level projections and informing long-term coastal adaptation planning across Pacific Island nations.