BUENOS AIRES, Sept 21, 2008 (AFP) - Argentina will face Rafael Nadal's Spain in the 2008 Davis Cup final after they completed a gripping 3-2 win over Russia in the semi-finals here on Sunday.

In-form teenager Juan Martin del Potro clinched the crucial final point when he eased past Igor Andreev 6-4, 6-2, 6-1 in the deciding singles, a result which gave the 19-year-old a 25th win in his last 26 outings.

Del Potro, with four titles under his belt this summer and with his only loss coming against Andy Murray in the US Open quarter-finals, secured victory with a smooth crosscourt winner.

'It's amazing,' said Del Potro. 'I served really well today and it's like a dream.

'If someone had told me in July that I would win four titles and reach the Davis Cup final, I would not have believed them.'

Argentina, who have never won the Davis Cup but were runners-up in 1981 and 2006, will enjoy home advantage in the November 21-23 final against two-time champions Spain.

The Spanish defeated defending champions USA 4-1 in Madrid to book a place in their sixth final.

Russia, who beat Argentina in the 2006 final in Moscow, had been 2-0 down after Friday's opening singles.

But they cut the deficit on Saturday when Igor Kunitsyn and Dmitry Tursunov defeated David Nalbandian and Guillermo Canas 6-2, 6-1, 6-7 (9/11), 3-6, 8-6 in the doubles.

In Sunday's opening singles rubber, world number six Nikolay Davydenko pulled Russia level at 2-2 when he defeated Nalbandian 3-6, 6-3, 7-6 (7/2), 6-0.

'I was playing very bad in the first set but I was fighting and fighting in the second, and I felt a different player,' said Davydenko.

Sunday's result was a disaster for world number seven Nalbandian who had come into this semi-final having won all of his 15 Davis Cup rubbers on home soil.

That record was extended to 16 with his win over Andreev in Friday's opening singles.

But the decision to play in Saturday's doubles, backfired as he ran out of steam in the fourth set on Sunday.

Nalbandian got off to flying start, breaking Davydenko in the fourth game on his way to clinching the first set.

He also broke the Russian in the first game of the second set but the dogged Davydenko broke twice in succession on his way to levelling the rubber.

In the third set, Davydenko broke in the fifth game and served for the set at 5-4, only to be broken back by Nalbandian much to the delight of the 14,000 fans inside the Estadio Parque Roca.

He held for 6-5 before Davydenko complained that his opponent was encouraging the crowd to chant excessively.

However Davydenko turned adversity to his advantage and stormed through the third set tiebreaker before Nalbandian wilted in the fourth set, paying a heavy price for playing three days in succession.