Ferran Torres scored a dramatic extra-time winne and shattered Lionel Messi's dreams of a triumphant farewell to football's greatest stage.
Barcelona striker Torres lashed home a thumping finish in the 106th minute to reward a dominant display by Spain against an Argentina team who failed to register a single shot on target in 120 minutes.
A star-studded crowd of 80,663 that included US President Donald Trump packed East Rutherford's MetLife Stadium to see if Argentina captain Messi could crown his glittering career with a second World Cup victory.
But the 39-year-old maestro, almost certainly playing in his final World Cup game, was reduced to irrelevance as Spain took control early on against an Argentina team who committed a catalogue of cynical fouls throughout.
The South Americans' skulduggery ended with midfielder Enzo Fernandez being sent off after a brutal challenge on Spain defender Pau Cubarsi in stoppage time.
For long periods though it looked as if Argentina may somehow hold on for a penalty shoot-out as Spain struggled to make the breakthrough.
A lofted cross to the back post by Pedro Porro found Williams who nodded into the path of Torres to crash home the goal that would clinch Spain's second World Cup title after their maiden 2010 triumph.
"Ultimately, the goal belongs to 47 million people -- not just me or the 26 players," goal hero Torres said, referring to Spain's approximate population.
"At the end of the day, all finals are tough; when you're up against Messi, there's a certain nervousness, but we always believed in our football and in ourselves."
Messi meanwhile was seen with tears streaming down his face after receiving runners-up medals at a trophy presentation headed by Trump, who was subjected to deafening boos and catcalls as he walked onto the pitch alongside FIFA President Gianni Infantino.
Trump and Infantino later presented the World Cup trophy to Spain captain Rodri -- the midfield general who had orchestrated La Roja's superb win.
"We have won everything, and that is wonderful," Spain coach Luis de la Fuente said of his team. "They are a generation of footballers who are a source of pride for Spain. Together, we are stronger."
Many fouls
There was an early sign of the South Americans' cynical gameplan early on when Alexis Mac Allister went flying in with a studs-up challenge that struck Dani Olmo's ankle.
Mac Allister escaped an early yellow card although after Slovenian referee Slavko Vincic only awarded a foul.
Spain made their presence felt moments later though, with Alex Baena poleaxing Messi with an elbow to the back that again escaped sanction.
Argentina continued to test referee Vincic's patience with a series of niggly challenges, and Nicolas Tagliafico was lucky not to be cautioned after raking Lamine Yamal's calf in a clumsy challenge.
Eventually, though Vincic did reach for a yellow card, with Lisandro Martinez booked for a cynical challenge on Mikel Oyarzabal.
The final's controversial extended half-time show featuring the likes of Madonna, Shakira and Justin Bieber stretched to 27 minutes but did little to upset Spain's rhythm.
The Spanish piled on the pressure in a lopsided second half as Argentina hung on grimly.
De la Fuente sent on Pedri and Ferran Torres for Fabian Ruiz and Oyarzabal and the chances continued with Argentina in full siege mode.
Pedri and Cubarsi both lashed long-range shots that Emi Martinez failed to grasp at the first attempt but somehow Argentina continued to hold on.
Late red card
Fernandez's reckless red card left Spain down to 10 men heading into extra-time.
Martinez had one last save deep in stoppage time when Yamal's superb whipped free-kick was clawed wide.
The Spanish dominance continued in extra-time, with Williams almost opening the scoring with a glancing header that Martinez got down well to save one-handed.
Moments later it looked as if Spain had made the breakthrough when Williams slid a low finish into the net but referee Vincic blew for a marginal foul on Nicolas Otamendi.
But the breakthrough came with Torres's winner.
Argentina made a desperate last raid on Spain's goal but La Roja held firm to seal victory.
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