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However, it was Watford that were looking the more likely to score against an indifferent Foxes outfit and the Hornets found a second goal when Deeney was first to a loose ball, but his shot was wild and failed to trouble Schmeichel.
City's best move of the opening stages came from Lloyd Dyer who, after exchanging passes with Drinkwater, crossed for David Nugent only for the ex-Portsmouth forward to hook his effort over Manuel Almunia's bar.
Nigel Pearson's side were punished for their inability to assert themselves on the game when Ikechi Anya laid the ball to Sean Murray, and his drive from the edge of the box was too good for Schmeichel.
Leicester managed to find an immediate response with time running out in the first half as Matty James swept home Ritchie De Laet's cross to pull a goal back for the Championship leaders.
The hosts went in search of an equaliser after the interval, but nearly fell further behind when Forestieri found himself in a good shooting position and instead opted to pass for Deeney, who couldn't reach the ball.
In desperation, Nigel Pearson sent on Chris Wood in attack as the Foxes looked for an equaliser and they piled on the pressure late on.
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It wasn't until the fifth minute of injury time that Drinkwater brought the leaders back on terms, when he unleashed a shot with the outside of his foot from 25 yards to beat Almunia to the relief of most inside the King Power Stadium.
The result sees Leicester move 11 points clear at the top of the table, but Queens Park Rangers can close the gap if they beat Derby County on Monday night