The Belfast team have an unassailable four points lead over the Co Down side with both having one game still to play.
Inst captain William Robinson hit two of the goals with Dane Ward and Stephen Kelso also on target with Luke Russell replying.
Meanwhile, Pegasus have one hand on the EY Irish Hockey League trophy after a comfortable 3-0 win over Cork Harlequins at the Dub.
A point against basement side Muckross on Saturday week will be enough for the Belfast side to lift the trophy for the first time in the league’s current 18-match format.
If they can do the business, then Pegasus will be back in Europe after a four-year absence, having last won the IHL in its abbreviated version in 2015.
Pegasus coach Greg Thompson declared: “I was happy with the performance and the clean sheet so all credit to the players.
“Our goalkeeper Megan Todd had to make a couple of saves but, overall, I thought we deserved the win.”
Lucy McKee gave Pegasus a dream start when she fired high into the net in the third minute after an incisive move, initiated by Shirley McCay and carried on by Taite Doherty.
Four minutes from the break, Ruth Maguire doubled the hosts’ lead when she netted a penalty corner switch.
Cork enjoyed their best spell of the game in the third quarter but were unable to make too many inroads against the watertight Pegasus defence.
With 12 minutes left, Alex Speers wrapped things up when she scored from close range following another set-piece.
Elsewhere, Belfast Harlequins kept their faint play-off hopes alive temporarily with a 3-2 win over Ards at Londonderry Park.
Brenna McEwen gave Ards a 1-0 interval lead from the penalty spot but goals from Lucy Geddes, Jenna Watt and Gemma Frazer put Quins in the ascendancy before Faye Kidd’s late consolation.
However, a 4-1 win for Cork over Ards yesterday means that the Belfast Quins can no longer reach the top four.
In IHL 2, Queen’s clinched top spot in Pool 1 after Emily McStea hit a hat-trick in a 6-0 win over Greenfields in Galway as the students moved emphatically into the promotion play-offs.
Ballymoney have gone three points clear at the top of the Ulster Premier League after a 3-1 win over Randalstown at the Joey Dunlop Centre.
Ballymena’s 4-1 loss to Mossley means they stay bottom, a point behind Town while Lisnagarvey kept their top-three hopes alive with a 7-2 win over Rainey.
In Senior One, Raphoe have been promoted to the top flight despite being held to a 1-1 draw by CI after Omagh lost 4-1 to Priorians.