La Roja are still reeling from Friday's 5-1 hammering, which left them facing an uphill struggle to qualify from Group B, and the new Chelsea signing says that Vicente del Bosque's men must take their chances if they are to get their campaign to retain their world title back on track.
"We know what we're playing for and against whom," the 27-year-old told Movistar.
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"The most important thing is to win and then, if we can score more than one goal, better. Then we'll have to play Australia."
Spain's humbling at the hands of the 2010 runners-up has led to questions over whether their time at the top of the game is over and has seen calls for a complete overhaul of the side but Fabregas insists that there is no need for wholesale changes.
"The boss will have his ideas about what he has to change and what he will leave the same but I don't think there will be a huge amount of changes because I think this side has shown how good it is," he argued.
"We are positive, even though it has been hard. I see the side fully focused on what they have to do, training well, with the right mentality. We have to win and get the three points, which are vital."