The idea to play Leonel Messi in midfield changed the history of Barcelona, a new BBC documentary dubbed Pep Guardiola: Chasing Perfection reveals.
The documentary states that Frank Rijkaard, the then-Barca coach opted to deploy Messi with some success as a playmaking number 10 and on the right wing.
However, it was Gurdiola who took over from Rijkaard, who arguably unlocked the eight-time Ballon d'Or winner's potential when he first decided to use him as a false nine in a match against Real Madrid in May 2009.
"Pep was watching Real Madrid games and he realised when the midfielders put pressure on the midfielders of the other team, the defenders stayed behind, therefore opening up a space of about 30 metres," reveals Sala-i-Martin, the former Barcelona board member and treasurer.
He said Guardiola then had the idea to play Messi "not in the centre-forward role" but, rather, "in the midfield, with 30 metres to run".
Former Barca assistant coach during Guardiola's tenure Domenec Torrent remembers wondering "why on earth" his boss wanted to mess with things in such a crucial game.
On the day, Barcelona recorded a historic 6-2 win over their most fierce rivals, Messi scoring twice. That season, they completed a historic sweep of La Liga, the Champions League and the Copa del Rey.
"That day I think changed the history of football, the history of Barcelona and the history of Messi," says Sala-i-Martin.
Until leaving the club in 2021 for Paris Saint Germain in France, Messi had spent his entire professional career with Barcelona, where he won a club-record 34 trophies.
The 36-year-old now playing for Inter Miami in the US Major League, boasts 10 La Liga titles, seven Copa Del Ray trophies and four Champions League gongs.
The Argentine also holds the records for most goals in La Liga (474), and most La Liga hat-tricks (36) and Champions League (eight).
Messi who guided Argentina to the 2022 World Cup glory, has scored 672 goals for the Catalans-the most goals by a player for a single club.
He has over 800 career goals for both club and country.