Two goals in the last 15 minutes from Chesterfield earned them a 2-0 win and crushed Harrow Borough's FA Cup dreams after the non-league side had threatened to cause an upset.
Goalkeeper Nick Jupp had been Boro's saviour after pulling of a string of sensational first-half saves but the Isthmian Premier side, three divisions and 86 places below their opponents, failed to find the net.
Spireites forwards Scott Boden and Jordan Bowery spurned chances early on as Harrow struggled to find their feet until Troy Hewitt's shot flashed across the League Two leaders' goal.
The part-timers were clinging on when Boro goalkeeper Jupp finger-tipped Ian Morris' drive onto the crossbar before the former Fulham prospect blocked when Bowery was through on goal.
Harrow winger Kenta Nakashami was denied a penalty after a heavy challenge by Spireites captain Dwayne Mattis before Jupp denied Danny Whitaker at point-blank range after Bowery's header cannoned off the crossbar.
The home side began to control the second-half but Troy Hewitt's header, which dropped wide, was their only near miss before Boden rose highest to head home Whitaker's corner after 74 minutes and break Harrow hearts.
Substitute Craig Davies notched his 13th of the season to secure victory by sweeping in Whitaker's cross in stoppage time.