Well....
At first level, a Wizard can disarm a fighter with a pretty high degree of certainty, if he can get two rounds in.
How?
Round 1: Cast True Strike
Round 2: Gripping whip in both hands (for the +4 bonus of it being a two-handed weapon) Disarm the Fighter.
Now, at 1st, the Fighter is probably using a two-handed weapon (+4), and maybe has a strength of, say, 16 (+3). With his BAB (+1), he's got a grand total of +8 to his attack roll in the opposed check.
At 1st, the Wizard has maybe a 7 in strength (-2), isn't proficient with the Whip (-4), but is holding it two-handed (+4) and is spending a True Strike on this (+20), and gets a bonus for using the Whip (+2) for a grand total of +20. If the Wizard rolls an 8 or better, RAW, the Fighter can't hold on to his weapon. So there's a 65% chance that the Fighter is simply weaponless. Of the remainder.....
If the Wizard rolls a 7, the Fighter needs a 20. On a 19 or less, the Fighter loses his two-handed weapon; the probability of the Wizard rolling a 7 and the Fighter rolling 19 or less is 0.05*0.95. If the Wizard rolls a 6, the Fighter needs a 19 or 20. The probability of the Wizard rolling a 6 and the Fighter rolling the 18 or less to lose his weapon is 0.05*0.90, and so on, down to the Wizard rolling a 1 and the Fighter needing a roll of 14. So the overall chance, if the Wizard gets those two rounds, of the Strength 16 Fighter-1 with a Greatsword of losing his weapon is: 0.65 + 0.05 * 0.95 + 0.05 * 0.90 + 0.05 * 0.85 + 0.05 * 0.80 + 0.05 * 0.75 + 0.05 * 0.70 + 0.05 * 0.65 = 0.93 = 93%.
Mind you, the probability that the Wizard-1 will get two rounds to do this to the Fighter without help is somewhat less than that.....