The Christmas presents came early for The Owls with MacLean cashing in on dreadful marking to grab his treble and Kenwyne Jones made the most of an appalling blunder by keeper Andy Warrington to score the other.
No Rovers player came out of the game with much credit as they were unbelievably bad at both ends.
Last season's top scorer Gregg Blundell had a chance to give Rovers the lead in the first minute when he raced through following a superb Michael McIndoe pass but he placed his shot just wide of the mark.
Blundell had cause for regret when MacLean fired Wednesday in front in the ninth minute. The former Rangers striker was given time and space to control the ball close to goal following Lee Bullen's right-wing cross.
Blundell was presented with another great chance following more good work by McIndoe in the 20th minute but his touch let him down with only the keeper to beat.
There was more misery for Rovers two minutes later when Warrington dashed out of his box to try and clear a long throughball from Glenn Whelan but he missed the ball completely allowing Jones to tap home from 15 yards.
Wednesday had not really played well themselves at that stage and it might have been a different story if McIndoe had found the net instead of rattling the inside of the post with a cracking effort in the 43rd minute.
But the home side went from bad to worse as Wednesday romped to victory in the second half.
MacLean made it 3-0 in the 59th minute when more bad defending allowed Jones to cross the ball from the right to set up the chance.
He completed his hat-trick with 14 minutes left when he was again left unmarked to head home Lee Peacock's right-wing cross with the defence all at sea.
It was the first league derby between the South Yorkshire rivals since 1956 and the result was a massive disappointment for the home fans in Doncaster's biggest crowd for 20 years.