The home side had the first chance of the game when Karl Darlow tipped over David Nugent's goal-bound header.
Forest were unable to make much of an impression on the Leicester goal and Chris Cohen's cross that sailed into the arms of Kasper Schmeichel summed up their start.
Nugent headed over another chance, but it was the away side who opened the scoring against the run of play as Simon Cox squeezed the ball past a defender on the line.
Jeffrey Schlupp volleyed the ball wide as the Foxes pushed for an immediate response.
However, Forest again punished Leicester on the counter-attack as Jamie Mackie stroked the ball into the top corner.
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The visitors continued to look dangerous on the counter, with Mackie beating his man and forcing a corner.
The Foxes had a great chance to get themselves back into the match, but Nugent fired a penalty over the bar.
Gary Taylor-Fletcher could have made it interesting but he missed when well placed.