Two goals from striker Leon Clarke helped Sheffield United to a thrilling 4-2 win at local rivals Sheffield Wednesday in the first Steel City derby for five-and-a-half years.
United made a devastating start and led after only three minutes when Tom Lees fouled David Brooks just outside the area.
The visitors conjured a superb free kick routine that saw the ball backheeled to John Fleck, whose low effort bent past the wall and flew into the corner.
And they doubled their lead after a quarter of an hour when Wednesday's offside trap fell apart as a ball was hooked over the top and Clarke, a former Owls player, slid home a cool finish.
Wednesday were struggling to offer anything much in return and were in danger of conceding a third as the visitors played by far the sharper attacking football.
Clarke fired wide and Chris Basham sent a difficult volley over the top, but out of nothing the home side secured a crucial lifeline in first-half stoppage time.
There seemed little danger when Jed Wallace, faced by defenders, got the ball on the right, but he dug out a cross that Gary Hooper guided inside the near post with a neat first-time strike.
Wednesday, who brought on Lucas Joao on for David Jones at the break, began the second half at a frenetic pace, and United's on-loan Spurs defender Cameron Carter-Vickers was soon forced to make a crucial interception as Wallace crossed dangerously towards Hooper.
Brooks fired over from outside the box as United tried to restore their two-goal lead, and then the same player produced an outstanding moment of skill to find the unmarked Clarke who, after bringing the ball under control, shot over.
It looked as though he would be made to regret that miss soon afterwards when substitute Joao seized on a low cross inside the penalty area to equalise -- but within seconds United substitute Duffy turned past a defender before finishing from an angle to restore his side's advantage.
Barry Bannan sent a long-range strike over and Brooks had a shot well stopped by Keiren Westwood as a compelling match continued to swing from end to end.
But Clarke had the final say when he bagged his second and United's fourth, muscling his way between two defenders to dink the ball into the far corner in the 77th minute.