Leicester City 1 Bristol City 2
The visitors took the lead early on when Maynard found the bottom corner from a free-kick and could have been 2-0 ahead just before half-time had Maynard not rattled the crossbar with a penalty.
The Foxes equalised through David Nugent's 25 yard second-half strike, but Sean St. Ledger's critical slip on the half-way line allowed Maynard to play the ball past Kasper Schmeichel to restore The Robins' lead.
It was a missed opportunity for Leicester to bounce back to winning ways after the weekend, while Keith Millen will have been delighted with his side's first win of the season.
Sven-Goran Eriksson made five changes to the starting eleven that lost 2-0 to Reading on Saturday - including captain Matt Mills being dropped to the bench.
But despite the adjustments, it was the visitors who had the first chance on goal when Gelson Fernandes conceded a free-kick on the edge of the area - a chance which was converted when Neil Kilkenny laid the ball off to Nicky Maynard who crashed the ball into the bottom corner from twenty yards.
It was the worst possible start for a home side demonstrating a lack of confidence, and proved to be a real setback for the remainder of a very difficult first-half.
David Nugent created some space in the final third just before the half hour mark, but dragged his shot wide of the far post.
The key point in the first period occurred just before the break when Gelson Fernandes was adjudged to have clipped Jamal Campbell-Ryce in the penalty area, with referee Nigel Miller awarding the visiting side a penalty.
However, Maynard struck the crossbar with the resulting spot kick, which seemed to spark Leicester into life as Paul Gallagher hit the target moments later with a free-kick at the other end of the pitch.
The Foxes came out looking stronger after the break and were almost level through Andy King's point-blank header, but goalkeeper Dean Gerken made a fantastic save to keep the visitors in front.
But it only took the hosts ten minutes to find an equaliser when Paul Gallagher dispossessed Neil Kilkenny in midfield before finding David Nugent, who found the net with a neat curling effort from 25 yards - his first as a Leicester player.
It was a much deserved goal for the former Portsmouth striker after being isolated for most of the match with very little support elsewhere.
Leicester tails were up and they should have taken the lead when Lloyd Dyer's pinpoint pass to Paul Gallagher gave the forward plenty of time to tee up a strike, but the Scot could not hit the target.
Suddenly, against the run of play, Sean St. Ledger was dispossessed just inside his own half, allowing Nicky Maynard to bear down on goal and, despite the last ditch efforts of Sol Bamba, find the net for the second time in the match.
It was a tough break for the Foxes who had shown resilience to find themselves level, but was also an indication of why manager Sven-Goran Eriksson has shown interest in Maynard during the transfer window.
Leicester set about finding an equaliser and came agonisingly close when Richie Wellens' cross-turned-shot sailed over Dean Gerken and hit Lewis Nyatanga on the line before bouncing back into the grateful hands to the goalkeeper.
But with time running out, Bristol City substitute Kalifa Cisse had a chance to put the game out of sight after some poor Leicester defending, but was wasteful with his effort which flew over.
Ryan Taylor then cleared the crossbar in stoppage time before Sol Bamba miscued a last-ditch shot wide of an open net after Neil Danns had forced Dean Gerken to spill the ball in a dangerous area.
Boos rang out at the final whistle - and with an imminent derby day at Nottingham Forest ahead, Eriksson will know things must improve to relieve any pressure upon him.
Man of the Match - Nicky Maynard