Argentina achieved revenge over Nigeria for their 1996 defeat with a narrow victory in the Olympic final in the blazing heat of the Bird's Nest stadium.
Lionel Messi, the 21-year-old Barcelona player whose participation in the tournament was threatened after his club won a legal battle with Fifa, proved the pivotal influence laying on a goal for Angel di Maria and regularly tormenting the Nigerian defence.
Everton's Victor Anichebe came closest to an equaliser for Nigeria but was twice denied by some brilliant goalkeeping.
Victory meant Argentina had buried the ghost of 1996, when they lost 3-2 to a Kanu inspired Nigerian side, and became the fourth country to defend their Olympic crown after Great Britain (1908, 1912), Uruguay (1924, 1928) and Hungary (1964, 1968).
It also meant two Olympic gold medals for Liverpool midfielder Javier Mascherano, the only survivor from Argentina's side in 2004.
Unlike 1996, this final was no classic though matters improved after a cagey first half.
Nigeria's Lokomotiv Moscow forward Peter Odemwingie had the first effort at goal, a tame long-range free-kick before Juan Roman Riquelme had a fairly woeful effort from his own free-kick in a much more promising position.
Messi kept threatening but Nigeria were snapping into the tackles, though African hearts were in mouths when the Barcelona forward threw himself over the foot of Chibuzor Okonkwo in the area, but referee Viktor Kassai of Hungary was not impressed.
Nigeria started to be more adventurous with Odemwingie looping a header over the crossbar and then sprinting past Pablo Zabaleta down the left. Argentina were in all sorts of trouble from his cross, but the ball ricocheted off Promise Isaac and keeper Sergio Romero was able to claim.
The closest to a goal in the first half came right at the end when di Maria unleashed a vicious strike that Nigerian keeper Ambruse Vanzekin did well to turn aside.
Messi had been kept quiet but five minutes after the break he finally showed his class.
A great first touch allowed him to skip past a challenge and he curled in a left-foot shot but Vanzekin managed to parry it.
But Messi was irrepressible and played a key role in Argentina's goal. It was his quick feet that gave him space to roll a perfect pass into the path of di Maria.
The Benfica midfielder showed a clean pair of heels to the Nigerian defence and as Vanzekin advanced to meet him hit a delightful chip over the keeper and into the net.
Anichebe came off the bench and came close with his very first touch but was blocked out.
Messi continued to threaten, playing through Sergio Aguero who was denied by a vital challenge by Onyekachi Apam.
The defender then was equally good to halt Messi in his tracks as the forward looked set to apply the coup de grace.
There was time for Anichebe to come within millimetres of an equaliser - he got a great touch to divert a cross inside the near-post but Romero just got a hand to it, and then managed to stop it rolling over the line.