Facing elimination against a side ranked nearly 60 places below them and with question-marks over their unity, they roared back with headed goals from veteran defender Jan Vertonghen and the much maligned Marouane Fellaini.
Then, with the clock ticking towards 94 minutes and limbs aching, they broke downfield one last time, kept their heads and set up substitute Nacer Chadli to guide home the winner.
There simply aren't enough suitable adjectives for this game.
Villain
Neymar may have scored one of Brazil's goals and created the other but his shameful, ongoing histrionics overshadowed that.
As he lay prone on the turf for the umpteenth time at this tournament, a Mexican opponent inadvertently trod lightly on his ankle, causing an appalling display of feigned agony and despicable theatrics from the Brazilian star.
Neymar's antics in this tournament have already spawned countless Internet memes and he was again widely (and rightly) derided for his latest display.
Imagine being one of the best players of your generation with skill and pace others could only dream of, but instead being remembered for embarrassing and pathetic play-acting.
Stat chat
The last team to come back from two goals down to win a World Cup knockout game was West Germany against England in the 1970 quarter-final.
Before today, Japan had never scored a goal in a World Cup knock-out match.
Belgium made 10 changes to their starting line-up, the most at a World Cup since Spain made 11 changes for their game against Saudi Arabia in 2006.
At 18.60 metres, Jan Vertonghen's opener for Belgium is the longest range headed goal at the World Cup since stats started being kept in 1966.
Both of today's games were goal-less at half-time, meaning 21 matches at this World Cup have been 0-0 at the break, but just one has finished that way.
Mexico have lost all five of their World Cup games against Brazil, without scoring a single goal.
Brazil's goals were their 227th and 228th in World Cups, taking them past Germany to the top of the all-time World Cup goalscoring list.
At 39 years and 139 days, Mexico's Rafael Marquez became the oldest outfield player to start a World Cup knockout match since Stanley Matthews (39 years 145 days) for England v Uruguay in 1954.
They said what?
Martin O'Neill, Ireland manager and pundit (on Neymar): "His reaction? Oh, it was pathetic. It was absolutely pathetic, honestly... I mean, the pain threshold of Neymar is just incredibly low, I must admit. I wouldn't like to see him coming out of the doctor's surgery after getting a flu injection."
Juan Carlos Osorio, Mexico coach: "I would like to thank our fans and apologise that we didn't accomplish our goal and I'm sorry about that. They are the definitely the best fans in the world."
Did you know?
Mexico have now been eliminated in the round of 16 at every one of the last seven World Cups.
What's next?
The quarter-final line-up will be completed tomorrow with the last two round-of-16 clashes.
At 2am (NZT), Sweden meet Switzerland in St. Petersburg before England take on Colombia in Moscow from 6am.
