Real improved in the second half and deservedly levelled through Marco Asensio in the 67th but the game swung back in Sevilla's favour in an extraordinary turn of events.
Real launched a quick counter and Benzema earned a penalty when he was felled by goalkeeper Bono, but a VAR review led to the referee penalising Real defender Eder Militao for an earlier handball and awarding a spot kick to Sevilla instead.
The own goal, in the third minute of added time, was the final twist in a huge weekend for the title race after Atletico had stayed top by earning a 0-0 draw at Barca on Saturday.
The stalemate at the Camp Nou offered title holders Real the chance to top the standings and leave their fate in their own hands although they went into the game in low spirits after their Champions League semifinal exit to Chelsea on Wednesday.
Real coach Zinedine Zidane shook his starting 11 up by dropping Eden Hazard after the Belgian's poor display in the 3-1 defeat at Stamford Bridge and was without captain Sergio Ramos, ruled out with injury in a season riddled with fitness setbacks.
His side were poor in the first half but looked to have gone ahead when Benzema leapt to turn in an excellent cross from right back Alvaro Odriozola, who had been left out against Chelsea in favour of Vinicius Jr in a makeshift wingback role.
The goal was chalked off though as Odriozola's foot was a couple of inches offside although the incident was overshadowed by the second VAR review in the second half of an entertaining contest with so much at stake at the top of the standings.