McSally, a former fighter pilot, had been favored to prevail over the two conservatives who have split the anti-establishment vote. Despite competitive primaries in both parties for the Senate races, the GOP outdrew Democrats 456K/361K, at least so far.
The contest could be critical to the balance of power in the Senate in November because the Arizona seat of retiring Republican Jeff Flake, a Trump critic, is considered one of the two top takeover targets for Democrats, along with Nevada.
McSally's strategy was one of necessity: Kelli Ward, the arch-conservative local lawmaker, and Joe Arpaio, the controversial former Maricopa County sheriff, ran against McSally by casting her has as a fake conservative, hoping to fire up the Republican electorate that helped deliver Trump the state in 2016.
With the hard primary finally behind her, McSally turned her attention to Sinema at her election night party, lobbing Trump-style attacks. If she wins in November, Sinema will become the first bisexual elected to the U.S. Senate and only the second openly LGBT person to be elected to the Senate.
Businesswoman Barbara Barrett, 67, is a former US ambassador to Finland who unsuccessfully ran for Arizona governor in 1994 as the first Republican woman to seek that office.
"Hollywood Sinema, I like to say that - Sinema with a 'C, '" she said.
The three-term Republican congressman who makes frequent Fox News appearances is known as an immigration hard-liner in a state where Hispanic voters hold outsized sway.
If those margins hold up when the precincts fully report, it looks like Arizona will remain a red state in November - perhaps especially with McSally leading the ballot.
The GOP total came to nearly 35 percent of what Trump won in Florida in 2016.
Flake's tweet included a photo of a $100 check that he and his wife wrote to Doug Jones, the Democrat who prevailed in the Alabama special election, over Republican Roy Moore. Beyond the raw vote totals, the GOP count also was a larger share of its last presidential election turnout.
The nation's eyes are on Arizona and its hotly contested U.S. Senate race, seen as a prime pickup opportunity for Democrats fighting to retake control of the chamber and challenge President Donald Trump's agenda on everything from illegal immigration to taxes and trade.
Polls have shown a close race.
With only token opposition in her primary, Sinema, a 42-year-old Tucson native, has been free to run essentially a general election campaign for months, positioning herself as an independent voice and eschewing attacks on Trump by name.
Pragmatic centrists are hoping for Gwen Graham, the former congresswoman and daughter of Florida political icon Bob Graham, who served as governor and senator. She won her primary Tuesday night.
Former Oklahoma City Mayor Mick Cornett and mortgage company executive Kevin Stitt will go against each other in the GOP gubernatorial runoff.
Sinema, a former Green Party member, has undergone her own political shift toward the middle over the years, joining the "Blue Dog Coalition" of moderate Democrats after winning her seat in 2012 and voting against Democrat Nancy Pelosi's re-election as minority leader in 2016.