In difficult conditions in Cloonacool, Kieran Kilkenny’s side took control of this tie from early on, and finished strong to win by five points.
Offaly did reduce the gap to just two points on several occasions, but Sligo pushed on to ensure the victory.
It took six minutes for the game’s first score, with Eoghan Rua’s Leah Duffy firing Sligo ahead, quickly followed by Tara Breheny’s goal from close range to bring Sligo four points ahead.
Offaly did respond though, with scores from Caoimhe Lynam and Anna Grehan, but Gavan Doyle’s side were guilty of missing chances that could have seen them go ahead.
Michele Mann’s shot was saved by Ellen Maguire, while Meabh Rouse then fired wide.
The home side extended their lead on 16 minutes when Denise McGrath’s effort was punched clear by Lauren Dunne in the Offaly goals, but Lauren Normanly was on hand to fire into the net.
A lovely passing move from Sligo was finished off by Sarah Cunney, to bring the hosts 2-3 to 0-2 ahead.
But Offaly responded to keep within touching ditance.
Lynam’s free dropped short, and Mann was lurking nearby, firing past Maguire, with Lynam then firing over for a point moments later.
A great save from Lauren Dunne in the Offaly goals denied Sligo another goal after a move involving Ellen Giblin and Sinead Regan.
The sides exchanged scores, with Roisin Mealiff’s point before half-time the last score of the half, with Sligo going into the break leading 2-4 to 1-5.
Both sides continued to add points after the restart, and Offaly were denied a certain goal thanks to an outstanding block from Cara King.
The CT Gaels player got her body in the way as Roisin Ennis set up Eve Kelly for a shot on goal.
In what was a low scoring half, Sligo added three further scores before the end of the game, bringing their second-half tally to just five points, while Offaly managed just the two points in the second period.
The result means that Kieran Kilkenny’s side have confirmed their spot in the semi-finals, and will take on Wicklow this weekend in their final group stage game.
The game is away from home, and their semi-final details will be confirmed in due course.
Sligo: E Maguire, C Dunne, A Durcan, T Breheny, C Walsh, R McGoldrick, S Cunney, C King, D McGrath, S Feeney, L Duffy, A McDaniel, L Normanly, E Giblin, S Regan.
Offaly: L Dunne, S McGuinness, F Dempsey, N Buckley, F McDermott, E Maher, A Grehan, R Mealiff, M Rouse, R Ennis, C Lynam, M Byrne, S Fitzgerald, M Mann, E Hand.
Referee: A Clogher.