Will Ferry was the home hero with a decisive derby double as Dundee United comfortably beat Dundee 3-0 at Tannadice.
The wing-back netted in both halves and also provided an assist for Ryan Strain's third goal.
Dundee had won the two previous derbies at the home of their city rivals but this time they were a distant second best.
The result leaves United still comfortably sitting seventh in the Premiership table while Dundee remain five points ahead of Kilmarnock in the relegation play-off spot.
The Terrors had a gilt-edged chance to take the lead in just the third minute when Zac Sapsford pounced on a mistake by Yan Dhanda and then ran through on goal but the Australian striker's shot was easily saved by keeper Jon McCracken.
The visitors then worked their way into a dangerous position but when the ball finally fell to centre-half Luke Graham, he blasted well wide of the target.
Instead, it was the hosts who made the breakthrough in the 14th minute. Ferry teed up Sapsford inside the Dundee box with his tame trundler taking a deflection off Graham before cannoning into Ferry, with the ball hitting the post and then rolling into the net.
The visitors came close to equalising when Dhanda sent a cross into the box towards Graham with his volley looking net-bound until a vital goal line clearing header by Iurie Iovu.
The pendulum swung United's way once again in the 24th minute when Max Watters found Neil Farrugia with a cross-field pass. The winger cut in and hit a low shot that McCracken made a hash of with the ball bouncing off the inside of the post before being cleared.
Dundee thought they had equalised in the 35th minute when Westley headed home from close range but the away support's celebrations were cut short when referee Matthew MacDermid was called over to the VAR monitor with the goal disallowed for a handball by Billy Koumetio.
Deep in stoppage time, Dundee captain Ethan Hamilton tried his luck with a long-range shot but it was held by goalkeeper Dave Richards.
There was a quiet opening to the second half with both sides struggling to carve out clear-cut chances.
However, United took total control of the game with two quickfire goals. In the 70th minute Ferry hit a low shot from the corner of the Dundee box which flew into the back of the net off the inside of the post.
Just two minutes later, the Terrors made it three with Ferry sending a superb cross in from the left with Strain bulleting a header past the helpless McCracken.
There was no way back for Dundee with the home fans celebrating the win and the attainment of the city bragging rights at the final whistle.
Jim Goodwin heaped praise on home hero Will Ferry for his derby masterclass in Dundee United's comfortable 3-0 win over Dundee.
Goodwin was delighted with Ferry's performance and also admitted that what happened in the previous derby at Dens, when the Terrors threw away a two-goal lead in stoppage time to only draw the game, acted as a huge motivational factor this time round.
Goodwin said: "We're really pleased with the end result. I thought the performance was really solid from start to finish.
"There's a bit of good fortune in the first goal. I'm not sure Will Ferry knew a great deal about it, but we'll take it.
"I'm delighted for Will. I think he started the season a little bit slowly and then grew into it. As the season went on, he got better and better.
"Of course, he's going to be on the radar of a number of other clubs out there. Thankfully, we've still got him under contract. I think we're in a very good position as a club."
And Goodwin insisted his team had a point to prove after the way the last derby ended.
He added: "Yes, I'm really, really pleased. I think it shows the character within the dressing room.
"A lot of people were saying to me in the build-up to the game during the week that it matters more to Dundee than it does to Dundee United because we've got nothing to play for and they do.
"But that's not the culture we're trying to create here. Over the last three years, we've driven home to the players the importance of every game."
Dundee boss Steven Pressley admitted the derby defeat was tough to take but acknowledged United were worthy winners. However, with Dundee still to secure their William Hill Premiership safety, he has promised a big response next week against St Mirren at home.
Pressley said: "Was it a bitter one to take? It was. I thought that the first half in particular was quite an even affair. I don't think there was a lot between the sides, but we never got going in the second half.
"In the end, Dundee United were definitely worthy winners."
Pressley added: "The real message is that we need to respond. We're hurting.
"It's always a sore one to take to lose a derby and to lose a derby 3-0."
