Linfield's title hopes suffered a huge blow as they were controversially beaten by Glenavon to drop nine points behind leaders Crusaders.
Eoin Bradley hit Glenavon's winner on 15 minutes with Linfield claiming that he had fouled defender Niall Quinn.
Linfield thought they had been awarded a penalty when Andrew Waterworth appeared to be felled but referee Raymond Hetherington waved play on.
After Matthew Clarke hit the woodwork, Linfield's Ross Clarke was sent off.
The defeat leaves Linfield nine points in arrears of the Premiership leaders with only five rounds of fixtures left and Crusaders also have a significantly superior goal difference to the Blues.
Speaking following the game, Linfield manager Warren Feeney conceded the title race to the Crues and congratulated Stephen Baxter and the squad.
The Mourneview Park match will primarily be remembered for three first-half incidents.
The first big talking-point was Bradley's 15th-minute goal as the Derry GAA star appeared to pull back Quinn before running clear to volley past Jonathan Tuffey.
Blues keeper Tuffey was in the eye of the next storm as he dropped a cross but had his blushes spared after Kevin Braniff had bundled to the net with the Glenavon striker apparently adjudged to have been offside.
Moment three came in the 35th minute as the Blues appeared to be denied a clear penalty.
Waterworth seemed to pay for his enthusiasm as he attempted to regain his footing after being felled but after he played the ball to a colleague, the subsequent effort was fired over the bar and there was to be no penalty for the stunned visitors.
Blues manager Warren Feeney later told BBC Radio Ulster that Hetherington had said there had been "minimal contact" during the incident.
Linfield's second-half efforts were mostly a case of long balls and huff and puff although Matthew Clarke did hit the woodwork from a free-kick.
Glenavon had several chances to put the match to bed with Bradley unable to get the ball out of his feet as Tuffey saved and Braniff then failing to beat the Blues keeper after the Linfield defence had been left stretched.
After having Ross Clarke sent off following his second yellow card, Waterworth did have a last-gasp chance to snatch a point but Glenavon keeper James McGrath made a fine save.
McGrath was named man of the match but while his handling had been impressive, the honour probably should have gone to his impressive team-mate Rhys Marshall.