Pires said: "It's true that I had trouble getting going this season. I lacked energy and a lot of friends told me they thought I'd got thinner, I was down in the dumps. But that goal against Liverpool was a real wake-up call.
"That truly launched my season and things have gone well since."
The Reds will be hoping that the former Marseille midfielder will full short of the mesmeric performances he has shown of late if Portsmouth are disposed of to set up a last eight FA Cup clash with the Gunners.