Glentoran moved up to fifth in the table as two goals from Steven Gordon helped them to victory at the Oval.
Gordon rifled into the roof of the net from six yards out after Stefan McCusker dropped a 15th-minute corner.
Gordon then tapped in from close range after meeting Curtis Allen's pass on 37 and Allen found the top right hand corner with a fine finish after 74.
David Kee grabbed a late consolation for the Mallards, who remain ninth in the table, a point ahead of Institute.
The Glens dominated the opening half and deservedly went in two goals up at the interval.
In addition to Gordon's two goals, David Scullion had a shot cleared off the line by Mark Stafford and Allen's left-foot shot skimmed the bar.
Gordon had an opportunity to complete a hat-trick but his back-post header was palmed away by McCusker.
Allen's finish from 10 yards was his 12th of the season and by the time Kee eventually unlocked the Glens defence, the points were secure.
Glentoran manager Eddie Patterson: "We're delighted to get the three points. I thought from start to finish we deserved what we got out of the game.
"We were unfortunate not to come in three or four goals up at the interval and it was just disappointing to concede that late goal."