Dundee United surged to the top of the Scottish Premiership by thrashing Dundee at Dens Park to leave their rivals without a derby win in 10 years.
Jackie McNamara's team were far too strong for Paul Hartley's side, who finished with 10 men after Thomas Konrad's dismissal late on, having gone into the televised meeting undefeated in six league games.
The Tangerines took over top spot in the league thanks to Mario Bilate's first-half penalty and further goals after the break from Ryan Dow, Callum Morris and Keith Watson, with Greg Stewart scoring an injury-time reply for Dundee.
There was plenty at stake as the home side attempted to end their long wait for a derby win that stretched back to 2004, while United knew they could go top by winning by three clear goals.
United settled the quicker and, 10 minutes in, Craig Erskine made some space for himself firing in a shot from 20 yards that the goalkeeper Kyle Letheren was relieved to see clear his far post.
But their efforts paid off as they swept into a deserved 24th-minute lead. Paul Paton dispossessed Jim McAlister 30 yards from goal and surged forward to give the ball to Gary Mackay-Steven, who powered into the hosts' area before Konrad halted him in his tracks. The referee Steven McLean was up with play and pointed immediately to the spot and booked Konrad. Bilate made an expert job of the resulting penalty to sweep the ball past the diving Letheren.
Soon after John Rankin tried his luck for the hosts from distance from Mackay-Steven's lay-off, but saw his effort go high and wide. It was end-to-end stuff and, with the last piece of action in the first half, McAlister headed over from Stewart's free-kick after Paton had been booked for a foul on Philip Roberts.
However, in the 54th minute Dow made it 2-0 to United. Rankin robbed McAlister and fed Dow, who strode forward and fired an unstoppable low left-footed shot past Letheren from 16 yards.
After 59 minutes United killed the contest by making it 3-0 in simple fashion. Paton's curling free-kick was the perfect height for Morris, who rose unchallenged to power a header past Letheren and into the corner of the net.
There was no stopping United now and they went further in front on 79 minutes. Paul McGowan's foul on the substitute Stuart Armstrong near the corner flag led to Paton flighting an inch-perfect free-kick to the back post, where the full-back Watson climbed high to nod into the net past Letheren.
To make matters worse for Dundee, Konrad was then sent off for his second bookable offence following a foul on the United substitute Scott Smith after 89 minutes.
Stewart struck a consolation goal for the visitors after 89 minutes with a low shot past the United keeper Radoslaw Cierzniak from 20 yards, but it made no difference.