Republican presidential front runner Donald Trump and Democratic favourite Hillary Clinton continued their wins, picking up Arizona on Tuesday, as the primary race shifted to the United States west coast.
But their rival contenders, too, received a boost.
Texas senator Ted Cruz momentarily halted Mr Trump's march towards the nomination by scoring a decisive win in Utah, after a dismal showing a week ago.
Vermont senator Bernie Sanders took Utah and Idaho - a much- needed boost for him to stay in the race and try to narrow the delegate gap with Mrs Clinton.
Commenting on the Democratic race, experts said that they do not believe Mr Sanders' twin wins will be enough to keep him in the race for long.
At this point, it looks likely that Sanders will no longer be viable by then.
POLITICAL SCIENCE AND LAW PROFESSOR TAEKU LEE, from the University of California Berkeley, on the Sanders campaign remaining hopeful about his prospects in key Democratic states like California
Though he may have enough campaign funds, Professor Barbara Norrander from the University of Arizona's School of Government and Public Policy said that "at some point, Clinton will probably win the 50 per cent of delegates needed for the nomination before the last primaries are over".
Political science and law professor Taeku Lee, from the University of California Berkeley, noted that Mr Sanders' success so far is "limited to states with relatively small black and Latino populations".
And while the Sanders campaign remains positive about his prospects in key Democratic states such as California, Prof Lee said: "At this point, it looks likely that Sanders will no longer be viable by then."
As the candidates swing through the states during the primary season, they pick up delegates who will select the party's nominee during the convention in July.
After Tuesday, Mrs Clinton has 1,681 of the 2,383 delegates required to win the nomination compared with Mr Sanders' 927, according to The New York Times and the Associated Press.
Undeterred, Mr Sanders said that national polls have shown his campaign's progress in the race.
"When we began this campaign about 10 months ago, we were 3 per cent in the polls, about 70 points behind secretary Clinton. As of today, the last poll that I saw, we are five points behind," he said.
During her victory speech, Mrs Clinton addressed the deadly attacks in Brussels which have also raised security concerns in the United States.
"What happened in Brussels tells us how high the stakes are," she told a crowd in Seattle, Washington, which votes on Saturday.
"The last thing we need, my friends, are leaders who incite more fear," she said, referring to Mr Trump's comments suggesting that the US rethink its involvement in Nato, and Mr Cruz's call for law enforcement to step up policing in Muslim neighbourhoods in the US.
"What Donald Trump, Ted Cruz and others are suggesting is not only wrong, it is dangerous. It will not keep us safe," said Mrs Clinton.
Prof Norrander said "Trump's hard line on the US-Mexico border would be a big concern among Arizona voters", which might have contributed to his win.
Arizona shares a border with Mexico and Mr Trump has continually talked about building a wall between the two countries to keep illegal immigrants out.
After Tuesday, Mr Trump's delegate count is 739 of the 1,237 delegates needed to clinch the nomination. Mr Cruz has 465, a sign that efforts by establishment Republicans to stop Mr Trump have been futile.
"Unless the 'Stop Trump' campaign discovers the silver bullet... Trump is poised to win most of the remaining contests over the next month," said Prof Lee.