The Arizona Supreme Court declined to extend a deadline for voters to fix errors with mail-in ballots.
The top court's ruling came as the state's Senate race was called for Democrat Ruben Gallego, marking the second major defeat for Republican Kari Lake.
On the other hand, voters in the state chose President-elect Donald Trump over Democrat Kamala Harris.
Trump's win is a reversal from 2020, when Joe Biden became the first Democratic presidential candidate to win Arizona since the 1990s. Biden narrowly flipped Arizona by about 10,000 votes.
While Trump won by a comfortable margin of about 180,000 votes this time, Lake lost her race by about 70,000.
This year's election results were tallied much faster than in 2020, but the nation was still waiting on Arizona and Nevada until the weekend. Both states make heavy use of mail-in voting.
Left-leaning groups, such as the American Civil Liberties Union, made a request Saturday to Arizona's Supreme Court to allow more time to "cure" mail-in ballots with errors. The petitioners asked for a four-day extension, arguing thousands of voters could be disenfranchised by delays in ballot processing.
Justice Bill Montgomery, however, said there was no evidence that voters were denied a "reasonable" opportunity to fix their ballots, which is required by state law. The court found that election officials in eight of the state's 15 counties had adequately informed voters of issues with their ballots.
"The Court has no information to establish in fact that any such individuals did not have the benefit of 'reasonable efforts' to cure their ballots," Montgomery wrote.
Lake, a former news anchor, became a rising star on the right in the 2022 midterms cycle, when she lost a close race to Governor Katie Hobbs (D).
Lake never conceded the race, which she alleged was impacted by malfeasance with ballot printers that disenfranchised Republican voters on Election Day. Last week, the Arizona Supreme Court rejected Lake's final appeal in her effort to challenge her 2022 defeat.
Ruben Gallego, a Marine vet and Democratic congressman, has defeated Lake for the open Senate seat vacated by Kyrsten Sinema. Lake has not conceded the race yet.
Republicans also failed to flip Senate seats in Nevada, Wisconsin, and Michigan. But they still regained the U.S. Senate and kept the House, leaving President-elect Trump with a "trifecta" to pursue his agenda in January.
