The Bulgarian football website www.bgfootball.eu said Ivanov scored the fastest own goal by a substitute in European club competition on Thursday with some statisticians claiming it was the quickest ever own goal by a player coming off the bench.
Ivanov headed the ball into the Levski net in the 87th minute with his first touch to level the scores at 2-2 just six minutes after Vladimir Gadzhev had put the home side ahead.
"This is the worst moment of my life," Ivanov, who replaced Macedonian international Darko Tasevski, told Reuters on Friday.
"I still don't have any explanation. I just wanted to clear the ball but I connected awkwardly with my head and it went in. It was so painful to see.
"But I want to express my admiration of my team mates, coaches and the incredible fans, of course, as they supported me in this difficult time," said 25-year-old Ivanov, who joined Levski from Beroe Stara Zagora in June.
Levski fans chanted Ivanov's name after the final whistle while he was wiping tears from his eyes.
Sporting Lisbon top the standings in Group C with nine points from four matches, followed by Lille on five. Levski and Belgium's Ghent have four points each.
"No one should blame Ivanov," said Levski sporting director Gerogi Ivanov. "This is part of the game. He has to overcome this difficult moment and we're here to help him."
Ivanov was instrumental in helping Beroe win the Bulgarian Cup last season and was named Best Bulgarian Defender for 2009.
He made his Bulgaira debut as a second-half substitute in the 4-1 win away to Malta in a friendly last November.
British record books claim Torquay United central defender Pat Kruse scored the fastest own goal in history - taking only eight seconds to find his own net against Cambridge United in a Fourth Division match in January 1977.
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