Dundee United recorded their second derby win of the season over Dundee with a convincing victory at Dens Park.
Keith Watson dived to head home Barry Douglas's corner before Dundee's Steven Milne volleyed over from close-range.
The home side were denied a second-half penalty after Brian McLean's handball.
An innocuous foul on Stuart Armstrong led referee Willie Collum to award United a controversial spot-kick that John Daly scored, then Willo Flood added a deflected third.
Dundee made their intentions clear by applying some early pressure originating from good wing-play on both sides.
Steven Milne released Nicky Riley down the right-hand side and he got the better of Barry Douglas to cause the first fluster in the visitors' box before Flood cleared.
Almost immediately after, Jim McAlister showed his capabilities down the left, skilfully knocking the ball past Keith Watson and crossing for Milne, but Gavin Gunning got there first to clear.
From the resultant corner, Riley had Radoslaw Cierzniak in the United goal worried for a second with a high looping header from the edge of the box that landed on the roof of the net.
It took until the 15-minute mark for United to apply any sort of real pressure.
Flood turned inside Kevin McBride before dinking a cross into the box, but Milne headed away. The header fell to Stuart Armstrong, whose 20-yard effort was deflected for a corner.
From that set-piece, United took the lead on 17 minutes.
Douglas clipped the ball left-footed to the near-post and Watson darted to connect with a diving header that had enough power to negotiate its way past three Dundee defenders on the line.
It was definitely against the run of play, but United were not caring about that.
A few minutes later, the first yellow card of the afternoon went to the Tangerines' left-back, Douglas, after a blatant trip on Riley as he cut inside on the right.
The home fans were on their feet in the 26th minute when McAlister's high flicked pass found John Baird. The forward met it with a header, but Cierzniak saved before realising the offside flag had been raised.
Shortly after, Dundee had a fantastic chance to equalise.
Matt Lockwood's whipped cross found the head of McAlister, who nodded to Milne, but he volleyed left-footed over the bar from eight yards out when he should have hit the net.
Rab Douglas's hands were warmed by another stinging Watson effort from long-range, then a terrific cross by Douglas attacking on the left led to Johnny Russell heading narrowly wide.
Russell looked lively again on 36 minutes, scurrying through the middle of the park towards goal as he shrugged off challenges. Eventually, he met the onrushing Douglas just inside the box and the ball was cleared.
Armstrong ensured the second half got off to a frenetic start by latching on to Russell's reverse pass to shoot low, but Douglas was equal to it.
Immediately after, there was a huge penalty claim from Dundee.
Baird's cross clearly hit the lower arm of Brian McLean and the home fans were astonished that referee Willie Collum did not award a spot-kick.
On 50 minutes, livewire Russell smacked the post after capitalising on a dreadful clearance by Declan Gallagher.
After the hour-mark, Dundee again pushed for the equaliser.
Iain Davidson's fizzed shot wide did not trouble Cierzniak, but Lockwood's 25-yard free-kick on 68 minutes certainly did, as the Polish keeper dived to his top-right corner to save.
Referee Collum then caused a stir by awarding United a penalty on 71 minutes.
Daly's shot was smothered by Rab Douglas, but Collum felt Armstrong had been fouled by Gary Irvine while crossing that Daly chance.
The striker himself stepped up to convert convincingly into Douglas's left corner, making it 2-0.
Despite Dundee trying to revive the game, United killed it off.
Flood's shot from the edge of the box was deflected off Kyle Benedictus, Douglas touched it on to the post, but it came back and hit the goalkeeper again and rolled into the net.