JAAP Stam cut a frustrated figure on the touchline as he watched his side squander a two-goal advantage and miss out on the chance to record a third straight league win against Cardiff.
Royals enjoyed two strokes of luck when an own goal from Callum Paterson and a deflected strike from Mo Barrow but the hosts ahead before the break.
Tempers continued to flare in the second-half and Bluebirds' boss Neil Warnock was sent to the stands for protesting to the officials.
However, it proved to be the catalyst the visitors needed as they grabbed two goals in eight minutes to claim an unlikely draw.
Joe Bennett volleyed beyond Vito Mannone with seven minutes of normal time remaining after Paul McShane failed to clear his lines, before Lee Tomlin's equaliser in injury time was confirmed by goal line technology.
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