United were rocked on their heels by Banks' superb opening goal in the 15th minute. The striker was teed up by skipper Ritchie Humphreys, making his 600th league appearance.
Banks had one thought in mind, jinking past a challenge on the 18 yard line before letting fly with an unstoppable rising right-footed strike that beat Martin Rice despite the United keeper getting a hand on the shot.
The Spireites doubled their lead four minutes later following a loose pass which enabled striker Armand Gnanduillet to attack the goal from a central position again. Gnanduillet's shot went awry but, unfortunately for United, it fell straight to Jay O'Shea.
Rice made a brilliant save to deny O'Shea the first time but could do nothing as the Chesterfield player bundled in the second effort.