McCarthy had been shown red in the reverse fixture at Elland Road in December for his heated protests after Matthew Kilgallon's controversial goal in a 2-1 win for the Yorkshiremen.
In this game City were in front after just four minutes with Iain Hume celebrating his seventh goal of the season.
Eirik Bakke - starting his first game since August - pulled down Hume to concede a dangerous free-kick 25 yards in front of goal.
Joey Gudjonsson's free-kick was deflected off a defender into the path of the former Tranmere hit man who swept the ball home from eight yards.
But Leicester lost their lead and their skipper on 12 minutes, when McCarthy was shown a straight red card after he tangled inside the box with Rob Hulse after the striker had latched on to a Paul Butler pass.
Referee Ray Olivier ruled that McCarthy had been the last defender and therefore had to go.
City players protested long and loud, but after calm had been restored Robbie Blake stepped up to slot home from the spot with the keeper going the wrong way.
With McCarthy gone Danny Tiatto dropped back to help his defence but Leeds were unable to make much headway despite their extra man.
And it was the Foxes who finished the half the stronger with Tiatto finding time to join the attack and flash an 18-yard shot just wide.
After the restart depleted City continued to show admirable enterprise. Gudjonsson blasted a free-kick against a wall of defenders and Butler was panicked into heading a Tiatto free-kick behind for a corner.
Neil Sullivan was almost surprised by Gudjonsson's long-range effort, needing two attempts to control the ball .
The tiring Tiatto made way for Gareth Williams on 65 minutes, with Alan Maybury taking up defensive duties.
As the game wore on the visitors began to dominate possession against ten-man City, but a blue barrier continued to ensure Paul Henderson was adequately protected.
After Stephen Hughes' long-range effort drifted narrowly over City were denied what appeared to be a legitimate penalty claim of their own when substitute Chris O'Grady was held back inside the box by Stephen Crainey.
Leeds finally mounted their first serious threat of the second half on 84 minutes when David Healy's cross from the right was half cleared to Liam Miller, but he failed to get a clean connection and dragged his 12-yard shot wide.
City then had late chances to steal it, first substitute Williams put Hume through but he uncharacteristically miscued his shot and then in time added on Gudjonsson's free-kick deflected off a defender into the path of Williams who drove straight at the keeper from 20 yards.