- Argentina reaches Davis Cup final
- Beats holder Great Britain 3-2
- Leonardo Mayer wins deciding rubber
- Will play Croatia for the title
Mayer stepped in for the exhausted del Potro for the fifth and deciding match of the tie against Dan Evans, with the teams tied at two wins apiece.
Despite falling behind to Evans, the 29-year-old Argentinian recovered to win 4-6 6-3 6-2 6-4, justifying the decision of team captain Daniel Orsanic to field him ahead of the Olympic silver medalist.
Evans was also playing his first rubber of the tie, replacing Kyle Edmund for the reverse singles, but could not match the inspired play of his opponent, who has an 11-3 record in Davis Cup matches.
The enthusiastic crowd in Glasgow had been in optimistic mood after Murray, beaten by del Potro in a five-set and five-hour-plus classic Friday, showed his fighting quality with a straight-sets win over Guide Pella to level the score at 2-2.
Murray, the Wimbledon champion and Olympic singles gold medalist, had also paired with brother Jamie to win Saturday's doubles, seeing off del Potro and Mayer in four sets.
It gave Britain hope after falling 2-0 down on the first day, when Edmund lost to Pella.
Del Potro, who has battled crippling wrist injuries, was not risked by Orsanic, but will clearly be a key figure for the final in Croatia from November 25-27.
Croatia, the 2005 champion, clinched its passage against France when Marin Cilic beat Richard Gasquet 6-3 6-2 7-5 in the first reverse singles in Zadar Sunday to build a winning 3-1 lead.
Argentina, a losing finalist four times in the past 10 years, will be looking for its first title in the famous team competition.