Experienced striker Kevin Lisbie levelled for 10-man Leyton Orient in the sixth minute of injury-time against Sheffield United.
The hosts had Charlie Daniels sent off for a rash challenge on Lee Williamson, who had to be taken off.
Chris Porter put the Blades ahead after Ched Evans and Kevin McDonald saw their efforts blocked.
The O's equalised when visiting keeper Steve Simonsen punched Dean Cox's free-kick to Lisbie, who lashed home.
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Leyton Orient boss Russell Slade told BBC London 94.9:
"I can't comment [on the refereeing decisions] otherwise it would be a very long interview.
"But there are about 20 decisions that we're not too happy about - everyone in the ground knew why we were 1-0 down."
Sheffield United boss Danny Wilson told BBC Radio Sheffield:
"Well I have to say it was a scrappy game in all honesty.
"I think we had the clearest cut chances in the first half in particular and it was just a scrap, we had to make sure we got something out of the game.
"It was very frustrating because we've lost two points. Some of the decisions we made in the last few minutes were what caused the goal."