For much of an international career that began a decade ago at the age of 19, Oyarzabal has not enjoyed much of the limelight.
He missed out on the 2022 World Cup in Qatar with a ruptured anterior cruciate ligament (ACL) in his left knee.
But four years later – and before a World Cup debut – he was in the form of his life with 12 goals in 12 international appearances.
The double against Austria extended that run to 17 in his last 16 starts, with four goals at this tournament.
“His last two seasons, since he recovered, are the best of his career,” added Balague.
“Four goals in the World Cup – our most decisive player, no doubt.”
Spain memorably played without a recognised striker at Euro 2012, but Oyarzabal is now very much the focal point of their attacks with two excellent finishes against Austria.
“Sometimes people are in doubt about Spain because of the centre-forward, but Oyarzabal is doing the job,” former Spain defender Cesar Azpilicueta told BBC One.
“A few years ago, Oyarzabal was playing a bit more on the right wing and he has transitioned more into the middle.”
Since the start of last year, the only European player with more international goals than Oyarzabal is Norway striker Erling Haaland with 22.
He also became the first Spanish player to score twice in a World Cup knockout match since Emilio Butragueno against Denmark in the last 16 of the 1986 tournament.
The statistics are impressive, but it is not to say he is overshadowed by Lamine Yamal, with the 18-year-old playing a key role in Oyarzabal being able to shine.
The Barcelona forward’s excellent ball control and dribbling skills clearly unsettles defences and pulled the Austrian defenders towards him to create more space for Oyarzabal.
“When you have someone in your team like Lamine Yamal who attracts so much attention, you know you will get more space,” said former Germany midfielder Thomas Hitzlsperger.
“Oyarzabal uses that space, gets the ball, and scores goals.”