Swansea City suffered just a fourth league defeat of the season against Derby County at Pride Park.
First-half goals from Colin Kazim-Richards and Kamil Jozwiak were enough to seal only a third league win of the season for the Rams.
Steve Cooper had named an unchanged side following Saturday’s 2-0 victory over Cardiff City in the South Wales derby.
However, the sluggish Swans were unable to match those performance levels as they missed out on the chance to close the gap on Bournemouth and Norwich at the top of the Championship table.
They remain on 33 points from 19 games and are now winless against Derby in seven attempts.
The division’s lowest scorers having only found the net eight times this season, 22nd-place Derby had failed to record a victory in their last 12 in the league at Pride Park.
Nevertheless, Wayne Rooney’s side made the perfect start; taking the lead after just four minutes when Lee Buchanan helped Graeme Shinnie’s free-kick into the path of Kazim-Richards, who beat Connor Roberts to the ball and prodded it past Freddie Woodman.
Kazim-Richards had another chance shortly afterwards, with Kyle Naughton just doing enough to put him off, while Woodman tipped Jason Knight’s 20-yard volley onto the post.
The hosts, who had drawn four of their last five games, continued to control proceedings and doubled their advantage eight minutes before the break, as Jozwiak fired into the far corner after Martyn Waghorn cushioned a deflected cross neatly into his path.
The Swans – coming into the game off the back of three consecutive clean sheets – may well have trailed 3-0 at the break had Kazim-Richards’ powerful header not struck the crossbar.
Desperately seeking a response, Cooper made a triple change at half-time as he looked to bolster his attacking threat; introducing Yan Dhanda, Kasey Palmer and Ryan Manning, while Jordon Garrick also entered the action soon after.
But, despite having more possession, the visitors were unable to establish any of their natural rhythm against a stubborn Derby, who were eyeing a fourth consecutive clean sheet.
This was only a fourth defeat in 19 league games for the Swans, and their 10-year wait for a victory at Pride Park goes on.
Derby County: David Marshall (capt); Nathan Byrne, Andre Wisdom, Matt Clarke, Lee Buchanan; Krystian Bielik, Graeme Shinnie; Kamil Jozwiak, Colin Kazim-Richards (Jack Stretton, 90+6), Jason Knight; Martyn Waghorn (Duane Holmes, 73).
Subs not used: Kelle Roos, Craig Forsyth, Max Bird, Louie Sibley, George Evans, Kornell McDonald, Jamal Hector-Ingram.
Swansea City: Freddie Woodman; Kyle Naughton (Yan Dhanda, ht), Ryan Bennett, Marc Guehi; Connor Roberts, Jay Fulton (Kasey Palmer, ht), Korey Smith (Liam Cullen, 81), Matt Grimes (capt), Jake Bidwell (Ryan Manning, ht); Jamal Lowe (Jordon Garrick, 61), Andre Ayew.
Subs not used: Steven Benda, Ben Cabango, Viktor Gyokeres, Wayne Routledge.