From being ready to axe the Brazilian, Redknapp admits the keeper is now a crucial part of his long-term plans.
Redknapp said: "He's up there with the very best. When he came here Tony Adams, who had worked in Holland, said they'd signed the best goalkeeper in the world.
"I watch Dutch football on TV and it's a completely different game and it took him time to adjust.
His performance against Arsenal could not have been further from his displays when Redknapp first took over.
The Spurs chief added: "I always knew he had the ability. I spoke to [former PSV Eindhoven coach] Guus Hiddink and he said he nearly took them to a Champions League final in 2005, he's that good."