Fati an early ray of optimism for Messi, Koeman's Barcelona
A brilliant start to the season for the 17-year-old continued on Thursday with another goal, his third from Barca's opening two La Liga games, which have seen them score seven and concede none.
Add in Fati's first international goal against Ukraine last month, which made him Spain's youngest ever scorer, and the sense is of a teenager ready to be trusted now by both his club and his country.
He makes opposition defences sit deeper, nervous of his runs in behind, and gives the team a more direct alternative when possession becomes predictable.
It was the role intended for Ousmane Dembele but the France attacker's injuries have curtailed his opportunities and Fati has stepped into the void.
"Ansu is a great talent," said Koema last week. "There aren't many players at his age that have the level needed to play for Barca. He has to learn things but he has made his debut for the senior team for a reason.
"For me he is a player of the future but at his age today he is already very impressive."
Born in Guinea-Bissau but raised in Seville, where he moved aged six, Fati has a fearlessness that scares defenders but most impressive is his maturity, the ability to shoot with a cool head and make the right decisions under pressure.
"Ansu is young but he deserves to be playing," said Sergi Roberto after the 3-0 win over Celta Vigo on Thursday. "I hope he can keep it up."
'A star is born', wrote Mundo Deportivo but after an explosive start, he faded a little, in part because Valverde was determined not to ask too much from him too soon.
Fati the future
His body may not be physically ready for that demand and it would be a surprise if some degree of mental fatigue did not take its toll too.
Yet for now, Koeman has an infectious talent, providing Barca the boost to morale they so dearly needed, not only to blur the memory of the last few months but also to vindicate their new coach and his project.
When Luis Suarez was allowed to join Atletico Madrid, Messi vented his frustration with another swipe at club president Josep Maria Bartomeu.
On Sunday, Sevilla will certainly offer a much sterner test as Julen Lopetegui's side look to prove they are ready to play a more serious role in the title race this term.
Atletico Madrid have the same ambition, with Villarreal up next on Saturday following Wednesday's goalless draw at at Huesca. Real Madrid head to Levante on Sunday.
Saturday (All times GMT)
Real Valladolid v Eibar (1100), Atletico Madrid v Villarreal (1400), Real Sociedad v Getafe (1630), Elche v Huesca (1630), Valencia v Real Betis (1900)
Osasuna v Celta Vigo (1000), Alaves v Athletic Bilbao (1200), Levante v Real Madrid (1400), Cadiz v Granada (1630), Barcelona v Sevilla (1900)