“Not just the preparation for the World Cup, but the subsequent investments in the World Cup and I think the answers we have now are a wake-up call for a lot of people.”
The match marked the return of striker Larissa Crummer to her first international in more than two years after recovering from a serious broken leg.
Cortnee Vine started alongside Crummer and Brisbane Roar teammates Katrina Gorry and Emily Gielnik.
Defensively, youngsters Courtney Nevin and Charli Grant were paired alongside experienced Tameka Yallop, who took over as captain, and Clare Polkinghorne.
When they met Australia for the first time, Spain controlled the match throughout the match and seemed to beat goalkeeper Teagan Micah by a goal in the 17th minute, but was declared offside.
The Matildas came close to opening the scoring in the first half when Gorry hit the crossbar from 20 yards out.
The tireless work of Clare Wheeler and Emily van Egmond in midfield helped keep Spain in control early on, but they finally opened the scoring just before the break when Aitana Bonmati scored in the 44th minute.
One goal below the break, Gustavsson presented Jamilla Rankin for her international debut, while Micah gave way to Mackenzie Arnold and Princess Ibini returned to action with the Matildas.
The second half went down quickly for Australia, with three goals from Spain in 12 minutes, thanks to Mariona Caldentey, Esther González and Lucia Garcia.
Spain threw salt at the wounds in the last 10 minutes, when Garcia took his second in the 81st minute and Irene Guerrero made two more.
Gustavsson made a nice rush in the 66 minute, but was eventually stopped by Amy Sayer
Completing the list of Australian debutants, Sydney FC’s Taylor Ray was introduced in midfield instead of Gorry in the 75th minute.
Gustavsson said he always intended to take a different approach to each part, introducing more inexperienced players later.
“I want to be clear now, it’s not about blaming individual players for this loss. These players represent more of a situation we are in now,” he said.
“We finished the game with four players playing in the NPL and one player in college. And waiting for those players to match Spain is not fair to individuals.
“But I’m ready to receive this blow as a coach. I said that from day one, we need answers and we need investment in our program.”
The Matildas will face Portugal in the last match of the FIFA window on Tuesday at the Estadio Antonio Coimbra da Mota in Estoril.
with AAP