But Los Angeles County Registrar/Recorder officials said only 4,000 absentee and provisional ballots remained uncounted, with the final tally not expected until next week.
Gatto was officially sworn into his new position Thursday in Sacramento. The district encompasses nearly all of Burbank and Glendale, and includes some Los Angeles neighborhoods. He fills the vacancy created after former Assemblyman Paul Krekorian left the position for a seat on the Los Angeles City Council.
Ramani on Friday declined to make any comment beyond his concession statement, which thanked his supporters for helping to break the "chain of uncontested local races" in the district.
"Disenchanted with the status quo, Republicans, Democrats and Independents demanded a choice," he said.
His campaign manager, John Thomas, said Ramani had yet to make a decision on whether to campaign for November's general election, which will determine who will fill the seat for a full two-year term.
"He is leaving his options open, but he hasn't decided either way at this point," Thomas said.
He also defended Ramani against criticism that he took too long to officially concede the special-election race.
"It's only been a few days," Thomas said. "We think this was a timely response."
Ramani and Gatto on Tuesday won their respective primary party nominations for November's election.
Ramani's name will remain on November's ballot regardless, but a decision to stop campaigning would essentially make November's race uncontested.
Gatto has said he remains confident heading into November regardless of Ramani's decision.
"This was obviously a very, very good chance for his party to contest the seat, because the indication that we saw was Republican turnout was double," he said.
"I think it would be harder to make that same case in November."