Kasper Schmeichel was another hero for Leicester on the night. Leading through Nugent's 70th-minute strike, Foxes substitute Jamie Vardy untidily brought Boro captain Rhys Williams down in the area, but Schmeichel plunged to his left to superbly thwart Marvin Emnes.
The adverse weather conditions delayed Middlesbrough's arrival and the kick-off by 15 minutes, but Tony Mowbray's men begin brightly, with top scorer McDonald firing a snap-shot over in the seventh minute after George Friend's cross was partially cleared by City centre-back Michael Keane.
Chris Wood, looking to build on six goals in three Leicester appearances and a hat-trick last time out, collected a slack pass from Emmanuel Ledesma and tested Jason Steele in the Boro goal following Nugent's return pass.
Steele was a spectator in the 28th minute when Anthony Knockaert collected Wood's lay-off from Paul Konchesky's raking pass on the left hand side of the penalty area and unleashed a venomous left-footed shot which struck the underside of the crossbar, bounced down onto the far post and out to safety.
In the 37th minute McDonald was allowed room to drive goalward from 25 yards. Schmeichel pushed behind and thwarted Andre Bikey's header from the resulting corner.
Leicester ended the half the stronger, with Nugent twice drawing sharp stops from Steele and Keane rattling the bar when Wood stood up a chip into the six yard box.
They should have paid for their profligacy eight minutes into the second period as Ledesma's dinked finish dropped wide after a cute, flicked pass from Middlesbrough's Chelsea loanee Josh McEachran sent him clear.
The hosts responded by striking the woodwork for a third time, Wood planting a powerful header against the upright from Konchesky's centre.
Nugent did manage to beat Steele and his goalposts in the 63rd minute but was adjudged to be marginally offside when he stroked home Ritchie De Laet's pass.
There was no debate when the once-capped England striker clinically swept a half-volley into far corner after Wood dinked the ball into his path.
Substitutes Lloyd Dyer and Vardy might have added a degree of comfort to Leicester's evening, before the latter was left to thank Schmeichel for sparing his blushes.