It was their first in a league game at Saltergate since 1948 and few of the home fans could deny they were good value for the three points.
MacLean took his total for the season to 18 and Lee Peacock put away a late header to end any hopes of a late Chesterfield rally.
Mark De Bolla did manage a reply in the final minute but it was too little too late and could not spoil the afternoon for the travelling supporters.
Wednesday were always the more powerful team and they had threatened to break through on several occasions before MacLean pounced in the 15th minute.
A mistake by Ian Evatt gave Peacock a chance which Carl Muggleton saved and MacLean tucked away the rebound from close range.
Peacock almost scored a second minutes later but Chesterfield only threatened at set pieces.
MacLean's second 10 minutes after the break was lucky with Graeme Lee's far post header hitting the striker on the heel and he picked up a booking for his celebrations in front of the home end.
Chesterfield pushed Evatt up front to try and claw their way back into the match but the closest they came was a 25-yard drive from Shane Nicholson which was well saved by David Lucas.
The contest was settled 12 minutes from the end when Wednesday broke out to score a classic counter attacking goal.
Peacock played the ball out wide to John Paul McGovern and then got on the end of the winger's cross to loop a header over Muggleton from eight yards.
Wednesday could have had more goals but the final word went to substitute De Bolla who drove the ball into the roof of the net after Lucas made his only mistake when he dropped a cross.