Belgium manager Rudi Garcia shocked everyone with his line-up in the World Cup Round of 16.
Facing the co-host United States in a packed Seattle Stadium, he began without his three biggest superstars, with Kevin De Bruyne, Romelu Lukaku and Jérémy Doku all on the bench.
The decision was widely viewed as a massive risk, but it worked a treat for the Belgians.
A young, hungry team completely took apart the USA in an emphatic 4-1 victory, with striker Charles De Ketelaere the star of the night after scoring twice in the first half to silence the home crowd.
As attention now turns to a massive Quarter-final match against an impressive Spain side in Los Angeles, Garcia has some serious puzzles to solve.
He has to decide whether to stick to a winning side or restore the big guns, while also dealing with a costly injury.
Deconstructing the Round of 16 win and the Spain Dilemma
Against World Cup Co-hosts the United States, Garcia set up his team in a fluid 4-2-3-1 formation focused on high pressing and quick counter-attacks. Instead of using Romelu Lukaku as a traditional target man, Charles De Ketelaere started up front.
De Ketelaere constantly dropped deep into midfield to connect plays, drawing defenders out of position and opening up space for wide players like Leandro Trossard to exploit.
Behind the attack, the midfield covered incredible ground to protect a young, less-experienced defense.
However, Spain presents a completely different level of difficulty, with La Roja winning four of their five matches at this World Cup and boasting four consecutive clean sheets.
They play a smooth, suffocating passing game that leaves little room for error, and Garcia simply cannot copy and paste his previous plan for two major reasons.
A major problem for Garcia is the injury to Amadou Onana, who went off after just 21 minutes with what has now been confirmed as an ACL injury.
He was replaced by Hans Vanaken, who had a solid display and also got on the score sheet.
While Vanaken has the physical presence and has shown solid playmaking abilities, he lacks the speed and defensive tackling power of Onana.
Starting him against Spain's world-class passing trio of Rodri and Pedri risks getting completely overrun.
Spain also protect the ball perfectly and do not commit the defensive errors the USA did. To break them down, Belgium need top-tier individual magic alongside hard work.
Expected Changes for the Red Devils
Because of this tactical dilemma, expect Rudi Garcia to bring some of his rested superstars back into the starting lineup at SoFi Stadium.
Kevin De Bruyne did not play a single minute against the USA and is completely fresh. Against a structured Spanish defense, his world-class vision and long-range passing will be absolutely vital to opening up holes in the final third.
Simultaneously, Jérémy Doku’s pace out wide is the perfect weapon to force Spain’s attacking fullbacks to stay back and defend.
To cover for Onana, Garcia might bring in veteran Axel Witsel or adopt a more defensive 4-5-1 shape to help young center-backs Brandon Mechele and Nathan Ngoy protect Thibaut Courtois' penalty box.
Difficult Balancing Act for Garcia
Ultimately, a manager's success in knockout football is defined by finding the balance between rewarding form and respecting the opponent's unique strengths.
If Rudi Garcia completely scraps the blueprint that dismantled the Americans, he risks breaking his squad's fragile new confidence and chemistry.
However, if he blindly copies the exact same system without making corrections for the missing Amadou Onana, Spain’s midfield will pass circles around his team throughout the contest.
Finding the balance between Seattle's fearlessness and Los Angeles' tactical discipline will determine if Belgium can march on into the final four.
Benching the old guard against the USA proved to be a smart move that brought hunger and energy back to Belgium. While it proved they can win big games without relying strictly on old names, knockout football is usually about survival and adaptation.
Because of the void from Amadou Onana's absence and the sheer tactical perfection of Spain, Belgium will almost certainly change their lineup.
Expect a hybrid approach on Friday when Belgium face Spain in their World Cup quarter-final, combining the high-energy stars of the USA game with the world-class quality of a fully rested Kevin De Bruyne.