Bussi completed 48.007km at the Velodromo Bicentenario in Aguascalientes, Mexico, 1,800m above sea level.
She beat Steven's record, set in 2016, by 27 metres.
Bussi, a former international track and field athlete who competed in the world cross country championships, had made an attempt on the record last year but fell 400m short.
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She is only the fifth woman to attempt the record since the UCI revised the rules in 2014, having previously prohibited the use of modern track pursuit bikes.
"We've witnessed a wonderful achievement," UCI President David Lappartient said in a statement on Friday.
"I congratulate Vittoria and her team, which helped her rise to the challenge with success. It is excellent to see women athletes attack the UCI hour record time." (Reporting by Martyn Herman Editing by Toby Davis)
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