Cook, invigorated by his saved penalty, stormed through the Wrexham defence to power a shot at Okonkwo in the Wrexham goal. The Red Dragons keeper did enough to keep the ball out, but could only parry back into the Bradford forward's path and his rebound found the back of the net.
The late blow will be devastating for the Red Dragons who have now lost three League Two games in a row. Phil Parkinson's side were looking to capitalise on Bradford's mixed form of late to lift them closer to the automatic promotion places but will be left ruing several missed chances.
Wrexham began the game well, controlling most of the ball and creating several chances for strike duo Paul Mullin and Steven Fletcher. However, neither of the high-profile strikers could find a way past the impressive Sam Walker.
With both Walker and Okonkwo in top form and neither side looking likely to score, a stalemate appeared likely. At least until the final 10 minutes, when Bradford were awarded the penalty that was saved by Okonkwo's trailing legs and then the late Cook dagger silenced the Racecourse Ground.