Zan Vipotnik's goal was his seventh of the season
Hull City's hopes of avoiding relegation from the Championship were dealt a cruel blow as Zan Vipotnik's controversial penalty gave Swansea City a fourth successive win.
Referee Ben Toner awarded the Swans a second-half spot-kick for handball, although replays showed that Vipotnik's shot had actually hit Hull defender John Egan in the face.
Hull had chances to equalise and appeals for a penalty of their own rejected, before substitute Matt Crooks was sent off in added time for a second booking.
The result keeps Hull 20th in the Championship table, two points clear of the bottom three with three games left, while Swansea move up to 11th.
The Swans had been looking nervously down the table when the gap between them and the drop zone was just six points as recently as last month.
But this winning streak means they are now closer to the play-off places than the bottom three – and still have the slimmest, barely plausible, chance of finishing inside the top six.
And while Alan Sheehan's side are on an upward trajectory, they are having a major say in the battle for survival.
Having beaten strugglers Derby County and Plymouth Argyle during this run, Swansea's victory over Hull plunged the Tigers deeper into the mire.
That made for a strange scenario in which Cardiff City, second from bottom of the table, were cheering on their oldest, bitterest rivals before their trip to Sheffield United later on Friday.
There was little to set pulses racing during a slog of a first half at the Swansea.com Stadium, where the hosts dominated possession but did not create any clear scoring opportunities.
Hull were on the back foot for large periods and, with Sean McLoughlin already on a yellow card for an early foul on Swansea winger Ronald, head coach Ruben Selles substituted the defender before half-time to avoid a red card.
If the visitors benefited from lenient refereeing before the break, they were on the wrong end of a highly contentious decision early in the second half.
Vipotnik controlled Lewis O'Brien's cross with his chest inside the Hull penalty area and fired a powerful shot which hit Egan in the face but, as his arm was raised, referee Toner thought the defender had used his hand.
Despite Hull's vehement protestations, Toner pointed to the spot and Vipotnik sent Ivor Pandur the wrong way as he buried his penalty.
Hull responded well and could have had a spot-kick of their own when Lincoln Henrique fell under a challenge from Josh Key, but Toner ignored the away side's appeals.
Crooks and Charlie Hughes both forced Swansea goalkeeper Lawrence Vigouroux into saves as the Tigers searched for an equaliser.
Swansea also had a few half-chances to extend their lead, and any hope Hull had of dragging themselves back into the contest seemed to evaporate when Crooks received his second yellow card in added time.
This was the first time the Swans had won four successive games without conceding a goal since 2008.
Sheehan is still only caretaker head coach but, if his side can maintain this form, the Irishman will be in a strong position to get the job on a permanent basis.
Post-match reaction
Swansea caretaker head coach Alan Sheehan:
"I like winning. The feeling of a sell-out crowd, people are watching their team giving 100% in every action and isn't that what we all want from our teams?
"The game could have been done at half-time if we were more clinical but these are a difficult team to play against.
"We scored and tried to get the second and because we didn't, we had to defend for the last 15 minutes and our defensive structure as a team is incredibly pleasing."
On the penalty: "I didn't really see it now to be honest. I saw the players appeal for it. Either way I think we deserved to win the game."
Hull defender John Egan:
"It's hard to speak because it's so raw. They were on top first half and then obviously the penalty in the second half has decided the game. The ball has hit my face so I don't know how they've given the penalty.
"I don't think the ref gave it, I think the linesman gave it. I asked him to speak to the linesman because the ball hit my face so he can't be 100% sure. They didn't want to do that. It's a tough one to take.
"To lose a game in that manner is frustrating. It's a tough loss to take. We've three huge games left now, we've got to dust ourselves down and go again."
