The on-loan Arsenal striker converted from close range in the second half to seal the points for the Black Cats, as the Reds lose further ground on European qualification
Both sides struggled to produce clear-cut chances in a scrappy first half that barely improved after the break, despite Bendtner's winning goal.
Steven Gerrard and Andy Carroll were introduced late in the game by Kenny Dalglish but Liverpool continued to struggle for ideas and could not find an equalizer.
The result lifts Sunderland, at least temporarily, with West Brom and Norwich City playing on Sunday, up to eighth place while Liverpool lost further ground on the European qualification spots and remain seventh.
With Lee Cattermole and Stephane Sessegnon suspended following last weekend's fiery derby against Newcastle United, Jack Colback partnered Craig Gardner in midfield for Sunderland. Wayne Bridge made his first start since signing on loan in the absence of Kieran Richardson.
Sebastian Coates started alongside Martin Skrtel in the Liverpool defense, with Jamie Carragher on the bench. Gerrard and Stewart Downing were also rested so Dirk Kuyt and Craig Bellamy joined the starting XI.
Both Liverpool and Sunderland came into this game off the back of eventful – for different reasons – fixtures the previous weekend, and they seemed to be suffering something of a hangover in the early stages. Neither side got an early stranglehold on proceedings, with Luis Suarez plugging away with little support for the Reds.
The Uruguayan created probably the best chance of the half in added time, escaping Michael Turner and beating John O'Shea before seeing his shot from a tight angle saved by Simon Mignolet.
Otherwise, the first 45 minutes left much to be desired. Liverpool began the match with a five man midfield but failed to take advantage of their numerical superiority in the centre of the park, hitting hopeful long balls that were ineffective in the absence of Andy Carroll and also had a strong wind to contend with.
Martin O'Neill fielded Bendtner and Fraizer Campbell in attack for the first time but did not see too much early promise from the duo. The Denmark international peeled away from the opposition defenders with some success, occasionally finding space in and around the penalty area, but was not helped by the lack of creativity around him.
Bendtner did latch on to a long ball that beat Coates midway through the first half, but his low cross was deflected clear.
Pepe Reina will remember the Stadium of Light for the infamous beach ball incident and he was unfortunate once again here to concede the first goal of the match. Sunderland were the quicker side out of the blocks in the second half and were rewarded after 55 minutes.
Campbell received a pass on the edge of the box and turned to cut across Skrtel before firing a low shot against the post. The 24-year-old's effort proceeded to bounce off of Reina's back, back on to the post and out to the arriving Bendtner, who converted from close range beyond the stranded goalkeeper.
Suarez combined well with Jordan Henderson only to shoot wide shortly after the opening goal but otherwise the Reds' response was minimal. Gerrard and Carroll were introduced – somewhat belatedly, it might be argued – with 20 minutes to go as Kenny Dalglish sought to rescue a share of the points.
The early signs were encouraging, with Carroll nodding a pass into the path of Gerrard, whose shot from distance was held by Mignolet. That positivity quickly petered out, though, with Sunderland finding more and more space in the opposition half as Liverpool looked to push men forwards.
O'Neill's team lost Bendtner to injury late on in the game but survived a late chance for Kuyt to secure three points that take them within two points of their opponents, although Liverpool retain a game in hand.