Thomas O'Ware headed his 11th goal of the season to provide the Greenock men with a dream start early on.

But Ton missed chances to extend their lead and Simon Murray equalised in spectacular fashion in 51 minutes.

Blair Spittal added another from long distance to give the Tangerines the advantage in Friday's Tannadice return.

The winner of the tie will go on to play Falkirk over two legs in the play-off semi-final.

With the exception of a couple of unfruitful Thomas Mikkelsen efforts, the first half was all Morton's. The hosts looked buoyant and the visitors were hesitant.

With O'Ware's last goal coming in February, he was experiencing something of a goal drought by his own standards.

Thomas O'Ware (second from right) gave the home side the lead but the Ton could not make more of their first-half dominance

That changed in seven minutes at Cappielow when the centre-back met Lawrence Shankland's long throw-in in the six-yard area and made no mistake in directing it past Cammy Bell.

All of sudden it seemed Jim Duffy's men's miserable nine-game winless run towards the end of the season was history, as Ton looked bright and confident.

Michael Tidser cracked a 25-yard effort off the top of the crossbar after Willo Flood had surrendered possession too easily, then Gary Oliver nearly sneaked one in from close range at the near post when Jamie Lindsay picked him out.

United defender William Edjenguele was tentative and the home fans felt he fouled Oliver in the box as half-time approached, but referee Willie Collum waved play on.

Morton's undoing was not making more of their dominance in the opening 45 minutes.

Out of nowhere, six minutes after the restart, the potent Murray received Spittal's pass with his back to goal and 25 yards out. No sooner had the young forward turned before his stunning, arrowed strike had hit the top right corner to take his tally for the season to 15.

Flood's near-post shot was beaten away by Derek Gaston to provide further evidence the tide was turning.

Spittal's return to the fray after injury could not have come at a more crucial time. The former Queen's Park midfielder did not appear to be threatening anyone until he unleashed a low drive from distance that nestled in the bottom corner to complete United's comeback.

Greenock's finest were rattled and only offered a Shankland header that landed on the roof of the net as they tried to work out what had happened to a game they had been controlling.

But United held on to make it seven games unbeaten.

Despite holding a 2-1 lead, Ray McKinnon is wary of the threat Morton will pose when they visit Tannadice on Friday

Morton manager Jim Duffy: "We were on the front foot in the first half but fair play to United, they changed it in the second half with two up top and they dominated.

"Once Dundee United scored they controlled the game, our energy levels dropped and we just had to stay in the game. At 2-1, what we didn't want to do was lose another one and the tie would have been gone.

"If we get a goal [in the second leg], it's all square and we can go from there.

"We don't have the luxury of maybe changing things round to give us that bit of impetus when it's going against us and that showed today.

"We have to recharge the batteries and go to Tannadice on Friday, throw everything at it and give it a go."

Dundee United manager Ray McKinnon: "We didn't really have any quality up top in the first half but it was a fantastic response in the second half.

"We changed the system, got a lot of pressure on their back four and thoroughly deserved to win the game.

"We had to stop them getting long balls out over the top - that was their outlet. We did that.

"In the second half the players were outstanding and we scored two really good goals.

"Morton are a really dangerous side. We will show them all the respect they deserve.

"We deployed Simon Murray on the left in a 4-2-3-1 system but he didn't really have an impact on the game, so we put him up top and he made a real impact straight away."