Martin Gritton appeared to have won a closely contested match in difficult conditions with his 77th minute goal, but Sam Saunders bundled in a corner in the third minute of added time.
It means that Dagenham are now unbeaten in 11 away matches and although they left it late, a point was the least they deserved.
Both teams had struggled to cope with a strong swirling wind in the first half when incidents and chances were few and far between.
Chesterfield keeper Tommy Lee, who was to emerge as a key figure in the closing stages, saved well from Jamie Guy in the 14th minute, but apart from a Jack Lester shot on the turn which went straight at Tony Roberts, there was little else before the break.
It was certainly different in the second half as chances came and went at both ends.
Roberts did well to deny Drew Talbot when the winger was baring down on goal in the 52nd minute and did even better to turn a 20-yard shot from Lewis Montrose onto the crossbar in the 55th minute.
At the other end, Guy broke through on the right only to see his lob come back off the crossbar and a shot from Ben Strevens was deflected by a Chesterfield defender onto a post.
But just when it seemed that neither side would score, Dagenham's defence faltered when a low cross was only half cleared by Scott Griffith and Gritton drove in his third goal for Chesterfield from eight yards.
Dagenham then showed why they have been so impressive on the road by taking the game to the home side and it needed an outstanding save from Lee to prevent Doug Loft equalising in the 85th minute.
Chesterfield defenders threw themselves in the way of shots as they tried to preserve their lead but the pressure finally told when Matt Ritchie swung over yet another corner and the ball flew into the net off the knee of Saunders.