In a tournament which has provided entertaining and free-flowing rugby from start to finish, the Argentines had warmed up for the final with earlier wins over Canada A (56-29) and Uruguay A (71-7), while the Fijians had been equally impressive in beating USA Select (62-12) and then Samoa A (39-26), but the finest drama was saved for last.
After a tight and cagey opening to the final that produced only three points in 20 minutes from the boot of fly-half Juan Cruz Gonzalez, Argentina capitalised on a Fijian yellow card and Julian Dominguez Widmer and Gonzalez both scored tries in quick succession. Gonzalez converted both to make the score 17-0 at half time.
Fiji fought back brightly in the second half, Lepani Raiyala and Sitiveni Kunaga both scoring to make it 17-12, and when Raiyala scored again on 62 minutes the Fijians had their tails up and led for the first time in the match, 19-17.
Gonzalez nudged the South Americans back in front with a penalty, only for Raiyala's hat trick score to take the Fijians further in front at 26-20, with just 10 minutes to play.
However, in a finale befitting the high-scoring, breathless rugby the tournament had served up, the Argentines were to have to final say. In the 80th minute 22-year-old Pedro Ortega crossed to make it 26-25, and Gonzalez held his nerve impeccably to convert with the final kick and hand the Argentines victory, 27-26.
In the earlier matches on the final day's play at the Estadio Charrua, Samoa A led Canada A 21-10 at half time but trailed 21-22 with only eight minutes to play, before a late penalty and a drop goal by sevens captain Patrick Faapale sealed victory 27-22.
Tournament hosts Uruguay A then delighted the home support by outscoring USA Select seven tries to two to win their final match 47-15 and land third place overall.