League champions Bohemians went back on top of the Premier Division on goal difference above Cork City following a vital win in front of 5,388 fans at Turner's Cross.
In a close encounter, it always looked as if one goal would be enough to win the points and that goal came after a good Bohemians spell at the start of the second half.
Jason Byrne headed home a Glen Cronin cross after 55 minutes to win the three points and consign Cork to their first league defeat in eleven matches.
Bohemians, who defeated Cork in all three league meetings between the clubs last season, had to select their side without suspended defender Jason McGuinness, while striker Glen Crowe and defender Mark Rossiter were unavailable through injury.
Cork were without Pat Sullivan through suspension and his place at the back went to Neale Horgan who was returning from an elbow injury.
The home team also brought back Billy Dennehy into the starting XI. He took over on the left side of the Cork attack having recovered from a hamstring injury, with Guntars Siligailis dropping to the bench.
But City manager Paul Doolin was forced to make a very early substitution when midfielder Joe Gamble, who picked up an injury in the opening minute, was forced to limp off after seven minutes to be replaced by former Bohemians midfielder Stephen O'Donnell.
As expected, it was a close encounter between the two top teams in the country with the best chances in the opening half falling to the home club.
After 18 minutes a fine cross from Colin Healy found the head of Denis Behan but his effort was well saved by visiting goalkeeper Brian Murphy.
Moments later, Healy sent in a ball from the left wing which defender Ken Oman belted over his own crossbar.
Pat Fenlon's side waited until just before the half time whistle for their best effort, a shot from 25 yards struck by Paul Keegan which caught a defender and flew behind for a corner.
Behan went close again for the Leesiders just after half time. Jason Byrne then found himself in behind the Cork defence before firing a shot which was blocked by goalkeeper Dan Connor.
Keegan then guided a header for the corner of the Cork net, but the ball was clawed away at the last second by Connor.
Then came the lead goal. A good delivery from the right by Glen Cronin was powerfully headed into the Cork net by Jason Byrne for his 11th league goal of the campaign.
Cork had some late pressure and even sent forward their goalkeeper for a free-kick in stoppage time, but Bohemians stood firm to go back on top of the table.
Cork City: Connor; Horgan (Kiely 4), Murray, O'Halloran, Murphy; Lordan, Gamble (O'Donnell 7), Healy; Behan, Kuduzovic, Dennehy (Siligailis 77).
Bohemians: B Murphy; A Murphy, Powell, Cronin, Shelley, Oman, Carey (S Byrne 89), Keegan, Deegan, J Byrne (Fenn 84), Ndo (Brennan 75).
Referee: Dave McKeon (Dublin).
