Rossi was 75-for-75 in the qualifying rounds. Her lone miss came on the 18th shot of the 25-shot final.
Rossi's overall 99 topped the former overall world mark of 96 by Zuzana Stefecekova of Slovakia in 2006, and her qualifying score of 75 was one better than the 74 by Victoria Chuyko of Ukraine in 1998.
The former Olympic records were an overall 91 set by Finland's Satu Makela-Nummela in 2008 and a qualifying 71 by Daina Gudzineviciute of Lithuania at the 2000 Sydney Games.
After her final shot, Rossi wrapped herself in the Italian flag, while three other competitors were preparing for a tiebreaker to decide the silver and bronze spots.
Zuzana Stefecekova eventually won the silver medal, topping bronze-medallist Delphine Reau of France in the shoot-off. Alessandra Perilli of San Marino also made the tiebreaker but was the first eliminated, meaning her nation — which has appeared in the Olympics since 1960 — is still awaiting its first medal.