Maguire lashed home a sweet drive with his left foot in the 66th minute following earlier efforts from Hope Akpan and Lucas Akins for Nigel Clough’s Brewers.
Craig Shakespeare made nine changes from the starting XI who faced Wolverhampton Wanderers at the weekend, including returns for Andy King, Leonardo Ulloa and Vicente Iborra.
After an often hectic opening spell, which paid witness to a succession of marauding runs from former Foxes winger Lloyd Dyer, Burton took the lead after just 17 minutes.
Akins seized possession on the edge of City’s area and fizzed it across goal for Akpan to nod it back the other way, finding the bottom corner with a well-placed header.
Before Leicester could really settle, it was 2-0 to Burton when, 12 minutes later, Akins fortuitously collected the ball in the area and slid it beyond an outstretched Eldin Jakupović.
Shakespeare’s men recovered and looked dangerous from thereon. Mahrez was a constant thorn in the side of Burton’s tiring defenders while Ulloa and Ahmed Musa also carried considerable threats.
Maguire then replaced Wes Morgan at the break while Ben Hamer also came on for Jakupović.
City proceeded to attack their hosts’ goal in waves with goalkeeper Stephen Bywater having to be alert to efforts from King, Ulloa and Demarai Gray, who joined the fray in the 61 minute.
Five minutes after Gray's introduction, Leicester found a breakthrough with Maguire firing it into the net with a venomous strike inside the 18-yard box.
Burton’s goal lived a charmed life in the latter stages as King rattled the crossbar and young defender Darnell Johnson tested Bywater from close range to no avail.
Key moment
Once Demarai Gray came on, the 21-year-old wideman was intent on making an impact at a sundrenched Pirelli Stadium.
Gray was typically industrious on the left flank and carved open a host of opportunities for the Foxes to level the scores, playing a key role in Harry Maguire's 66th minute strike.
Who impressed?
Even in pre-season, scoring your first goal for a new club is a landmark occasion.
Harry Maguire is renowned for being an assured figure at the back. Following this performance, typified by his emphatic strike late on, his prowess in front of goal shouldn't go unnoticed either.
Up next…
Bundesliga side Borussia Mönchengladbach are City’s guests to King Power Stadium on Friday night (7:45pm kick-off).
Just seven days later, the real business starts with a Premier League curtain-raiser at Emirates Stadium against Arsenal to look forward to.