Having won their last four matches, Mexico were expected to comfortably overcome 106th-ranked Belarus at the Borisov Arena.
But Miguel Herrera's men were on the receiving end of a surprise defeat at the hands of their plucky hosts, who have claimed just one point from their opening four Euro 2016 qualifiers.
After a goalless opening 45 minutes, the match burst into life with four goals in the space of eight second-half minutes.
Atletico Madrid striker Raul Jimenez twice put Mexico ahead, but Syarhey Kislyak fired home an initial equaliser after Ihar Stasevich's missed penalty and Nikolay Signevich headed a second Belarus goal from close range.
The drama was complete in the 81st minute when Nekhajchik provided a composed finish from the left of the six-yard box to secure the win for Belarus.
Belarus belied their underdog status in the early stages and Igor Shitov fired an early warning when he stot wide from eight yards in the fifth minute.
Mexico grew into the game, however, and Giovani dos Santos could have had a penalty when he was tripped in the area, before Arturo Gonzalez was denied when one-on-one with Belarus goalkeeper Sergey Chernik.
Mexico's improvement continued after the break and they took the lead in the 47th minute, Jimenez controlling the ball on his chest and prodding past Chernik after collecting a wonderfully deft chip from Jonathan dos Santos.
Yet Belarus were back level within three minutes. Paul Aguilar was punished for a foul on Kislyak, who then fired home a rebound after Stasevich's penalty had been parried on to a post by Alfredo Talavera.
The breathtaking start to the half continued as Mexico moved back ahead in the 53rd minute, Jimenez coolly slotting home Giovani dos Santos' cross from the right, only for Belarus to strike back again when Signevich converted Anton Putsila's powerful cross two minutes later.
lIya Aleksievich should have won the game for the hosts when he skewed wide from six yards with the goal gaping.
But the miss did not prove costly as Aleksievich's deflected shot fell into the path of Nekhajchik, who calmly guided the ball into the bottom right-hand corner.
