An astonishing first-half display earned Dundee a first derby victory over neighbours Dundee United at Tannadice since 2004 and eased their Scottish Premiership relegation fears.

A bullet header from Jordan McGhee opened the scoring for the visitors and Scott Tiffoney doubled their advantage soon after, as his shot from long range squirmed horribly out of goalkeeper Jack Walton's grasp.

Glenn Middleton's curling left-footed strike halved the deficit for United, but McGhee whipped home his second before half-time to restore Dundee's two-goal cushion as their hapless hosts struggled to contain them.

Dundee could have led by more at the interval - two goals were chalked off for very narrow offside calls and Simon Murray fired inches wide on the turn after United failed to clear a corner.

However, having been comprehensively outplayed in the opening 45 minutes, United brought themselves back into the contest after the break as Kristijan Trapanovski's deflected effort nestled in the net.

Both sides had chances from there. Joe Shaughnessy's header bounced just over for Dundee, while Sam Dalby could not steer his own headed effort on target.

But as United threw on a succession of attackers in search of a leveller, Dundee struck the telling blow late on.

Substitute Emmanuel Adegboyega - by then United's sole defender - was shown a second yellow card for desperately shoving Murray in the box.

The Dundee fan picked himself up to seal the win from the spot before gleefully running the length of the Tannadice pitch to celebrate in front of the United fans.

"That's the performance we're capable of," Docherty said. "I take a huge amount of pride, not just in the result.

"We've won here for the first time in 20 years. There was a lot on that today. I saw the players' spirit and mentality. I had confidence and trust in them.

"It was a performance from a team that displayed absolutely everything."

It is Dundee's first league win since 5 January and their first top-flight victory at Tannadice since a 2-1 triumph under Jim Duffy in August 2004.

Tony Docherty's side move to within one point of Kilmarnock in 10th and are five clear of bottom side St Johnstone.

United, meanwhile, stay fifth, three points ahead of seventh-placed Motherwell with three games left before the split.

Docherty and his players were under serious pressure before the walk down the road to Tannadice.

They were winless in eight league outings and had shipped 24 goals in that time. St Johnstone were narrowing the gap as Dundee slumped.

Those struggles were cast aside for the derby as they raced out of the blocks.

Lyall Cameron found the net after Josh Mulligan's shot was parried by Walton, only for celebrations to be belatedly ended by a VAR intervention for a marginal offside against Oluwaseun Adewumi.

Dundee weren't put off by that disappointment though, McGhee powering a header back across goal after Ziyad Larkeche picked him out with a cross from the left.

The visitors poured forward time and time again and although Walton kept out Cameron's drive, the goalkeeper failed to get behind Tiffoney's shot moments later.

McGhee's finish to make it 3-1 was sublime, weighted to perfection, and only another VAR intervention prevented a fourth - Murray was spotted offside before the ball struck Ross Graham and found the back of the net.

Dundee's attacking excellence in the first half will hearten Docherty, but so too will their second-half resilience.

They weathered a spell of United pressure and it was fitting that Dundee fan Murray sealed the victory in stoppage-time with a cool penalty.

Perform like that until the end of the season and their top-flight status should be safe.

Dundee were superb, yes, but United manager Jim Goodwin will look back on the first-half concessions with dismay.

They looked rushed, panicked and overwhelmed by Dundee's fast start and coughed up possession in dangerous areas an alarming amount.

Walton made an uncharacteristic error for Tiffoney's goal and McGhee was twice left unmarked to score.

Adegboyega's decision to push Murray late on was a daft act, one borne out of his side's desperation to level perhaps, but he will now miss United's trip to Dingwall after the international break.

With the league as tightly packed as it is and only three matches until the split, Goodwin's side will be sweating over their league position.

A difficult visit to Tynecastle follows before they host St Johnstone, with seventh-placed Motherwell just three points back.

Dundee manager Tony Docherty: "We have been hampered with experienced players being injured, but we had experience in there today. You see more of the Mulligans, the Adewumis, the Camerons.

"We dug in. That pleases you more sometimes. They'll get the plaudits and they deserve that."

Dundee United manager Jim Goodwin: "The opening 45 period was completely unacceptable in every department.

"Every mistake that we made in the first half, Dundee capitalised on it. A free header for the first goal, a mistake from Jack Walton who has been outstanding all season, Will Ferry runs the ball [for the third]. All of those really avoidable on our part.

"We haven't been as bad as that all season. It's really out of character. We spoke about not having a repeat performance [of the cup performance at Dens] and for the life of me, it's so hard to put your finger on why."