It's extremely unlikely that rotation occurred (that is, the front wheels came off the ground due to elevator pressure having been applied) and then the main wheels remained on the runway. When the front of the aircraft lifts up, the relative position of the wings (and flaps of course) changes, providing enormously more lift, and the a/c becomes airborne virtually simultaneously.

Although I'm sure that you perceived the front wheels to have lifted up, and I obviously can't sit here and disprove that they did, it is far more likely that the change in G-force that pushes you back in your seat caused you to believe that the aircraft had rotated.