It depends on many factors, but I really think an anti-psion prepared wizard can have a significant edge.
For example, if the Wizard has Psychic Turmoil or Greater Psychic Turmoil in his repetoire and prepared, that can be a little bothersome to the Psion at real close range. For example, if the Psion wanted to do a touch power or a psionic weapon against the Wizard, he would have to go through this area in order to do that.
Also, Globe of Invulnerability will totally negate any 4th or lower level psionic power which tends to be about half of the Psion's powers.
If the Wizard can manage to attack the Psion with an Evards, PT, and GoI, the Psion might be in serious trouble if he does not have Teleport or Ethereal Travel of some kind (Astral Caravan, Ectoplasmic Form, or Dimension Door will not cut it). Once captured, the Wizard backs away and throws a Dimensional Anchor at the Psion and the Psion could be in big trouble. PT is placed on a point in space, so the Wizard could be some distance away protected, even behind a wall and still be taking out the Psion.
The Wizard would just have to remain hidden (Mind Blank, Greater Invisibility) and survive long enough to totally drain the Psion of PP (about 10 rounds, 20 if the Psion had not used any PP that day and uses none in the combat) whereas the Psion would not only be trapped and have to survive the Wizard's additional attacks, but he would also be unable to use half of his powers if still in the Globe. There are only a few powers that would allow a Psion to escape a trap like this (e.g. Timeless Body, Null Psionics Field in campaigns were magic and psionics are the same, etc.).
Granted, a Psion might be able to dispatch a Wizard as well, but the Wizard should win if he knows ahead of time (divinations) that he will be fighting a Psion. It is only when the Wizard is not prepared to fight a Psion where the Psion should have a significant edge.