Argentina squandered a two-goal lead and slipped to a shock 4-2 defeat to Nigeria in a friendly on Tuesday.
Lionel Messi was absent for the national team, which opened the scoring through Ever Banega and Sergio Agüero and seemed to be in a comfortable position with just 38 minutes gone.
Leicester City striker Kelechi Iheanacho pulled a goal back for Nigeria just before half-time with a free kick and Argentina's defence collapsed in the second half, eliminating the goodwill that had emerged after the national team’s last-gasp qualification for World Cup 2018 last month.
Arsenal forward Alex Iwobi scored twice as Nigeria stunned the Albiceleste in the friendly match in Krasnodar.
Argentina, who beat Russia 1-0 in Moscow on Saturday at the ground that will host next year's World Cup, left Messi out of Tuesday's friendly following an agreement with Barcelona.
Banega delivered the opening goal on 28 minutes with a well-struck free-kick after Nigeria goalkeeper Daniel Akpeyi was penalised for a handball outside his area.
Argentina promptly doubled their advantage when Agüero, who scored the late winner over Russia, converted a right-wing cross by Cristian Pavon, the Boca Juniors winger making his first international start.
But Nigeria, who went unbeaten throughout their World Cup qualifying campaign, refused to surrender and Iheanacho halved the deficit before the break with a 25-yard free-kick.
Iheanacho then found an unmarked Iwobi who equalised from close range on 52 minutes, with Amkar Perm defender Idowu drilling Nigeria into a 3-2 lead moments later.
Argentina's attempts to claw their way back into the match were ended when Iwobi grabbed his second goal on 73 minutes, taking a pass from Ahmed Musa and hammering home to seal just a second win over Argentina in eight meetings.
Argentina defender Javier Mascherano said: "Playing against a team of such physical strength you pay the price. They walked all over us... and when we tried to get back on the match we couldn't."
Victory over Russia
Saturday’s victory over Russia had delivered a more promising performance, with a late goal from Agüero securing a 1-0 victory.
A patient Argentina eventually managed to unlock a stubborn Russian defence on the ground that will stage the World Cup final next year, Moscow's renovated 81,000-capacity Luzhniki stadium.
"We came here to play against a very disciplined and organised side," Argentina coach Jorge Sampaoli said on Saturday. "We made some mistakes in the first half but in the second we improved. We played a very intense game.
The coach singled out Agüero for his performance.
"Agüero played very well," Sampaoli said. "He understood the philosophy of the game and was very active even though he didn't have much space."
However, the mood swiftly changed on Tuesday, when it became clear once again just how important captain Messi is the national team.
Worryingly, reports emerged post-match that Agüero had been rushed to a local hospital in Krasnodar after he fainted in the dressing room at half-time of Tuesday's friendly with Nigeria.
Local media reported that Argentina's team doctor took the decision to transport Agüero to hospital as a precaution and to undergo medical tests.
The Argentine Football Association (AFA) said on its Twitter account that the Manchester City forward "had a blackout and was taken (to hospital) so routine examinations were made only as a precaution."
AFA gave no further details on the incident. Local media outlets published pictures of Agüero walking out of the stadium, however.