Emmanuel Adebayor opened the scoring just after half-time with what looked like his arm but Cristiano Ronaldo equalised from the spot after William Gallas handled and Owen Hargreaves grabbed the winner with a precision free-kick.
Defender Ferdinand told Sky Sports: "There are more points to be played for, the title is not handed out yet.
"We have not many times been a goal down at home but we came back. We showed pure grit and determination and a great team ethic.
"We were maybe fortunate with the penalty but in the second half we looked more like scoring."
"I heard a shout of 'keeper', but Edwin (van der Sar) said he didn't say it, so I've left it and it's gone in," said the defender. "It was on my head really."