The striker fired Marco Silva's side to a third-straight win after a 1-0 Premier League victory at the King Power Stadium.
It left Fulham seventh in the Premier League on 28 points - the same amount they were relegated with in 2021 - and level with Liverpool.
The Cottagers are in dreamland, in contrast to the Foxes with boss Brendan Rodgers' consistent reality checks still ringing true after a third-straight defeat.
Rodgers has always been insistent this season would be one of struggle and his side have reverted to their early form which saw his own position called into question.
Youri Tielemans rattled the crossbar during an improved second half but it was Fulham's fast start which ultimately sealed the points.
Willian shot over inside the opening five minutes and he had another close effort soon after, curling just wide after Kenny Tete's break.
The Foxes had already lost Kiernan Dewsbury-Hall to injury minutes before kick-off, with Wilfred Ndidi coming in, and saw Boubakary Soumare limp off after just eight minutes.
Mitrovic also required treatment meaning the game struggled to get going - until the striker found the winner after 17 minutes.
Wout Faes' own-goal double gifted Liverpool victory last week and the Foxes again shot themselves in the foot.
Daniel Amartey needlessly gifted possession to Harrison Reed with Willian seizing the chance to cross for Mitrovic.
The striker peeled off the back of Faes, the defender caught ball watching, and he had time to control and finish neatly past Danny Ward.
It was Mitrovic's 11th goal of the season - equalling his best Premier League haul.
The hosts were restless but they should have been calmed when Tielemans teed up Ayoze Perez, only for the unmarked striker to blaze horribly over from six yards after 24 minutes.
It only served to increase the anxiety at the King Power Stadium, although Bernd Leno needed to be alert to beat away Jamie Vardy's centre with Harvey Barnes lurking.
Leicester were at their frustrating best as there were glimpses of a comeback without any serious sign they were going to haul themselves level.
They had improved from a poor start but were still jeered off at the break while Fulham looked comfortable.
Yet the visitors were almost undone five minutes after the restart when Luke Thomas produced a brilliant ball for Barnes but the forward could not lift his shot over the advancing Leno.
Leicester had begun to find space and the goalkeeper denied Vardy before Tielemans curled the ball wide.
Fulham held firm, though, and remain upwardly mobile with the impressive Reed central to their success.
Leno saved well from Perez with 13 minutes left and Tielemans went even closer three minutes later when a trademark half volley smacked the bar.
Fulham rode their luck but Harry Wilson had the chance to make it comfortable in injury time only to prod wide after sprinting clear.