US presidential candidates Donald Trump and Hillary Clinton were the projected winners of their parties' Arizona primaries Tuesday.
Bernie Sanders secured his victory in Utah.
The two front-runners in the US presidential race, Donald Trump and Hillary Clinton, had been expected to win the votes in the south-western US state.
With 58 per cent of the vote counted, Trump is ahead on the Republican side with 46 per cent of the vote compared with 22 per cent for his closest rival, US Senator Ted Cruz. Ohio Governor John Kasich had 10 per cent.
The billionaire businessman had been favored to finish on top and collect all 58 delegates. Trump's strong opposition to illegal immigration appears to have been well-received in the border state.
Clinton is projected to defeat her only rival, US Senator Bernie Sanders, in Arizona on the Democratic side. She had 60 per cent of the vote compared with 37 per cent for Sanders, with 71 per cent of the vote counted. The state's 75 delegates will be divided among the two candidates proportionally.
Multiple US media outlets projected Trump and Clinton would be the winners.
Voters were still weighing in late Tuesday in two other western states, Utah and Idaho, which are holding caucuses as opposed to the traditional ballot voting of a primary. Only Democrats were voting in Idaho.
Voters on American Samoa affiliated with both parties also were voting Tuesday.
Trump faces a tough challenge in Utah caucuses, where Cruz is favored to win. The overwhelmingly Mormon state is among the most conservative in the nation, and Trump has had difficulty wooing members of the church who are turned off by his brash style, multiple marriages and lavish lifestyle.
Mitt Romney, the 2012 Republican nominee, a Mormon with strong ties to the state where he oversaw the Salt Lake City Olympic Games in 2002, has come out strongly against Trump and urged voters to instead support Cruz.
Sanders is looking to do well in Utah and Idaho because he has had past success in states that hold caucuses.
Clinton and Trump lead the count of delegates needed to secure their party's nominations at conventions in July. But each still needs to win many more delegates in state-by-state voting in order to clinch their party's nomination outright.
Trump still faces strong opposition from within the party establishment and could face a challenge at the convention if he fails to win a majority of delegates before the meeting in July.