Hurst, back for his second loan spell from Sheffield United, smashed an unstoppable drive to the top right corner after Walsall had failed to deal with a low cross.
The visitors had twice been in front but Chesterfield showed the spirit that has made them one of the surprise packages in League One this season by bouncing back to take a point.
It would have been different if Kevin James and Mads Timm had put away clear chances in the second half but their finishing did not match Hurst's.
There were chances at both ends from the start with Chris Westwood clearing off the line from Jamie O'Hara while Barry Roche had to be at his sharpest to keep out a James header.
But James showed why he is one of the quickest forwards in the division in the 33rd minute when he raced away down the Chesterfield left before cleverly cutting inside past two defenders to set up Timm for a close-range finish.
But Walsall had struggled to cope with the aerial threat of Wayne Allison in the first meeting between the teams back in September, and the big striker again took advantage of slack defending when he headed a free-kick from O'Hara inside the right-hand post from 12 yards.
The scoreline was about right at half-time, but Walsall regained the lead five minutes into the second half with another well-worked goal.
They broke quickly from just outside their own penalty area and Timm glided through the middle before his perfectly weighted pass sent in Grant Smith who slipped the ball low past Roche as he came off his line.
It was an excellent goal but Walsall never looked secure at the back and it needed a brilliant double save from Joe Murphy in the 78th minute to keep them in front.
First he plunged to his left to tip away a low drive from former Saddlers midfielder Paul Hall and he then showed his agility by pushing over a header by Derek Niven.
Timm should have rewarded his keeper two minutes later when he was through on goal with only Roche to beat but he drove a shot straight against the former Nottingham Forest man.
The significance of that miss was highlighted seconds later when Chesterfield broke downfield, and when Niven played the ball in low from the right, Walsall only half-cleared the danger and Hurst drove a shot past Murphy.
Chesterfield looked capable of going on to win the game but Walsall managed to hang on despite a few anxious moments but they will look back on this as a missed opportunity to record their first league win on the road since September.