Leicester collected their first away win of the season with goals by Danny Tiatto and Iain Hume, while Paul Butler's late header proved scant consolation for Leeds.
After conceding ten goals in their last three matches, Leeds badly needed to shore up their defence, but they looked vulnerable long before Tiatto's opener on the half-hour.
Elvis Hammond twice went close for Leicester, firing just past the angle of post and bar after only ten minutes and shooting high over the bar from 18 yards.
Leicester suffered a blow in the 23rd minute when midfielder Gareth Williams limped off after a collision with Richard Cresswell.
But the Foxes showed no sign of losing their rhythm and slack Leeds marking inside their penalty box was punished when Tiatto rifled a left-foot shot into the top left corner.
It was 40 minutes before Leicester keeper Conrad Logan was tested and he proved equal to the task by scrambling David Healy's powerful 30-yard effort round a post.
Leeds, with 19-year-old winger Adam Johnson making his debut in place of Eddie Lewis whose wife had given birth earlier in the day, lacked a cutting edge.
Leicester should have scored again just before the interval but, with only Neil Sullivan to beat, Josh Low shot wide of the far post.
And Leeds rode their luck again two minutes after the break when Derry cleared Patrick Kisnorbo's shot off the line.
Leeds' woes continued in the 54th minute when Hume's long through ball threatened to release Hammond, who stumbled following Kilgallon's challenge inside the area. After consulting his assistant, referee Colin Webster showed Kilgallon the red card.
Sullivan produced a superb save from the resultant free-kick from Hume, who had another shot brilliantly turned aside by the Leeds keeper who spared his side from a heavier defeat.
Hume was eventually rewarded as he beat Sullivan with a low angled drive from the right on 81 minutes and, although Butler headed a consolation goal four minutes from the end, Leicester deserved their win.