Lee Hughes looked to have got the Magpies' revival back on track when he headed home David Martin's corner in the 64th minute, but with two minutes to go Nicholls grabbed his side a share of the spoils.
Hughes had also missed the best chance of the first half when Karl Hawley's square pass was passed on to him by Martin, and the veteran forward scuffed wide.
Walsall's Julian Gray flashed a shot inches off target before the first save of the night, when Craig Westcarr out-paced and out-muscled his marker but fired straight at Jimmy Walker.
Five minutes after Hughes' goal brought a scrappy second half to life, the Saddlers came agonisingly close to an equaliser. Oliver Lancashire's shot looked to be heading into the far corner, only to miss by a fraction.
But with just over a minute of normal time remaining, Walsall counter-attacked and Nicholls ran onto Matthew Richards' throughball and finished with aplomb.
Notts County 1-1 Walsall: Match Report - view commentary, squad, and statictics of the game as it happened.