Jason Scotland's 26th goal of the season moved the Swans another point closer to their Championship dream at Roots Hall.
Scotland slotted home a first-half penalty after Tom Butler had been brought down by Charlie Mulgrew.
But Hal Robson-Kanu snatched an equaliser five minutes into first-half injury-time to share the spoils and keep their own play-off hopes alive.
The draw extended Swansea's lead at the top to 10 points after second-placed Doncaster lost 2-1 at Yeovil.
Southend United:
Flahavan, Francis, Clarke, Barrett, Mulgrew, Black, McCormack, Bailey, Gower, Robson-Kanu, Walker. Subs: Collis, Grant, Moussa, Scannell, Barnard.Swansea City: De Vries, Austin, Tate, Bodde, Britton, Pratley, Scotland, Lawrence, Robinson, Rangel, Butler. Subs: Duffy, Tudur Jones, MacDonald, Bauza, Way.
Att: 9,797 Away: 896
Swansea received a welcome boost before the game when the news broke that all police charges against assistant-manager Graeme Jones have been dropped following an incident in the tunnel at Bristol Rovers on Tuesday.
His Swansea side had one change from the one that moved nine points clear at the top with a 2-0 win at the Memorial Stadium.
Manager Roberto Martinez brought back Leon Britton into a three-man midfield as he reverted to a 4-3-2-1 formation.
Striker Darryl Duffy was the player who made way as 25-goal Jason Scotland led the line, while Andy Robinson passed a fitness test on an ankle injury.
There were no changes at the back with Garry Monk (back) and Marcos Painter (hamstring) still out through injury, while striker Febian Brandy started a three-match ban for his red card at Bristol.
Southend named the same starting line up after Nicky Bailey and Charlie Mulgrew both recovered from hamstring injuries sustained in last weekend's win at Huddersfield Town.

Match report
The game started in difficult conditions at Roots Hall with a strong wing blowing across the pitch.
Southend started with the wind in their favour as an early shot from Mark Gower was easily saved by Dorus de Vries.
Swansea responded in the fifth minute when Dennis Lawrence met a Robinson corner with a header which Darryl Flahavan was well positioned to save.
Flahavan saved another effort from Scotland straight after before de Vries was called into action at the other end from Hal Robson-Kanu.
With 13 minutes gone, Mark Gower picked out Peter Clarke, but his header flew wide.
Swansea won another corner two minutes later which Tom Butler delivered, but Robinson's header flew over the bar.
Swansea were celebrating in the 22nd minute though as they were the first to make the breakthrough when a fantastic cross-field ball from Ferrie Bodde picked out Tom Butler.
The winger jinxed beyond Charlie Mulgrew who duly brought Butler crashing to the ground.
The referee had no hesitation in pointing to the penalty spot and Jason Scotland stepped up to hammer home his 26th goal of the season.
It was just what Swansea needed against a Southend side that were the form side in the division alongside Carlisle having lost just once in 10 games, including a six-game unbeaten run.
Once the game had settled down again, Leon Britton became the first player to go into the referee's notebook after the Swansea midfielder fouled Nick Bailey.
Southend's Tommy Black followed him soon after for a foul on Britton, but not before 'keeper de Vries had pulled off a brilliant save from Peter Clarke seven minutes before the interval.
The yellow cards were starting to flow now as Darren Pratley was booked for a foul on Bailey.
Then in first-half injury-time, disaster struck as Robinson gave away a free-kick for a foul on Simon Francis.
Mulgrew delivered it from the right and Hal Robson-Kanu arrived unmarked to thump a header beyond de Vries in the fifth minute of injury-time for his third goal in as many games.
It was the last piece of the action as the referee immediately blew his whistle as the Swansea players looked at each other in total disbelief.
Half-time: Southend 1 Swans 1

The Swans came flying out of the blocks as a great build up put Butler in, but his powerful shot was deflected behind for a corner before Southend cleared the danger.
But Southend weathered the early storm and came back strongly as a shot from James Walker was blocked by Tate.
Southend won their second corner compared to Swansea's eight, but Tate proved his worth again with a good clearance header.
Southend made the first change of the afternoon when Lee Barnard came on for Walker with 58 minutes gone.
Swansea were still to get into full flow with their passing, however, as Roberto made his first change straight after.
Striker Darryl Duffy came on for Robinson as Swansea switched to a 4-4-2 formation as Butler went to the left and Britton to the right.
Butler was straight into the action as Tate found him with a great pass which nearly matched Bodde's first-half effort. Butler cut inside to fire a shot just wide with 66 minutes gone.
Tate picked up a yellow card soon after for a foul on Bailey 30 yards from goal, but Swansea cleared the danger at the second attempt after good work by the experienced Kevin Austin.
Southend had the edge with 17 minutes remaining as a poor pass from Bodde to Angel Rangel let in Barnard. The substitute raced clear with Tate and Lawrence in pursuit, but he fired wide under pressure from the two central defenders.
It sparked Swansea into life as Pratley had a goal-bound effort blocked on the edge of the area at the expense of another corner, while Butler also came close.
And Swansea should have been ahead in the 77th minute when Bodde's cross-shot struck the bar. The rebound fell to Lawrence who failed to find the target and Austin's back-heel was cleared off the line.
As play started to swing from one end to the other, Barnard had a penalty appeal turned down before Owain Tudur Jones replaced Pratley in the middle of midfield.
Mark Gower brought a fantastic save out of de Vries with four minutes of normal time remaining, while Tudur Jones fired wide at the other end.
In the end though a draw was a fair result as Swansea immediately switched their attention to Easter Monday's derby against Bristol Rovers at the Liberty Stadium (5.45pm).


















