The Bit o' Red conceded a stoppage time goal to blow the title race wide open, leaving them just two points clear of second-placed Derry City
The hosts had the first chance of the game with David Cawley collecting the ball just outside the area and driving a low shot which drew a save from Drogs keeper Gabriel Sava. Cawley laid it off for Aaron Greene a few minutes later, but the midfielder got under the ball and it sailed over Sava's crossbar. At the other end, David Cassidy struck a long-range shot, but apart from that effort, Gary Rogers did not have much to do in the early stages.
On 23 minutes, Drogheda United took the lead against the run of play. David Cassidy's free-kick found Declan 'Fabio' O'Brien in the box, and the forward did well to send the ball past Sava. Premier Division top scorer Anthony Elding was getting himself into good positions up front for the Bit o' Red, but his efforts at goal were weak and didn't threaten Sava.
Sligo came out re-energised after the half-time interval, and dominated the early proceedings of the second-half. However, Sava had to do little in the Drogheda goal bar collect a cross from Pascal Millien which was intended for Elding. Elding did reach an Alan Keane cross minutes later, but couldn't direct his header on target.
The home side's dominance finally paid off on 66 minutes, with Anthony Elding getting up to head in Aaron Greene's cross for his 10th goal in 10 games. Just two minutes later, Sligo were a man down as Ross Gaynor received his marching orders from referee Anthony Buttimer for an off the ball incident.
Despite going a man down, Sligo battled for a winner, and it looked to have finally come in stoppage time as Danny Ventre squared for Aaron Greene after great play from Kieran Djilali, and Greene placed his shot into the net off the post.
Greene's late goal looked set to see Sligo take all three points, but Graham Rusk popped up in the fifth minute of additional time to beat Rogers.
The draw sees Sligo fail to extend their lead at the top of the Airtricity Premier Division table, with Derry City now trailing the leaders by two points.