Trump's victory, however, was overshadowed by the clashes between anti-Trump protesters and police outside his event in Albuquerque, New Mexico.
The win in Washington state where Trump received 76.2 per cent of the total votes polled brought him less than 10 delegates shy of clinching the nomination.
The victory -- winning at least 40 of Washington's delegates -- means 69-year-old Trump now has 1,229 of the 1,237 delegates he needs to clinch the Republican party nomination, according to CNN estimates.
In the primary, Trump garnered over 76 per cent of the vote as Texas Senator Ted Cruz and Ohio Governor John Kasich each earned 10 per cent of the vote, while retired neurosurgeon Ben Carson earned 4 per cent of the vote.
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Washington did not have enough delegates to put him over the line. However, its results do, however, leave him inches short of it with a slate of key contests on June 7 in California, New Jersey, New Mexico, Montana and South Dakota sure to seal the deal.
On the same day of his big win, Trump's rally in New Mexico turned violent as anti-Trump demonstrators clashed with police, hurling rocks and burning clothes at officers.
The "unlawful assembly" went on rampage, lighted fires and threw rocks at the police officers and their horses outside Trump's rally.
The protesters disrupted the real estate tycoon's speech several times. Most of the protesters were escorted out.
Trump is the only Republican candidate left in the race to the White House from the Republican party, which was crowded with as many as 17 candidates at the start of the primary season early this year.
While 68-year-old Clinton is likely to clinch the nomination because of the lead she has in delegate count, her opponent Senator Bernie Sanders from Vermont has refused to call off the race till the last vote in the primary election is cast.
Campaigning in California, Sanders told his supporters that he would not let Trump become the US President.
Sanders' campaign yesterday released a new television spot that will run in California ahead of the state's June 7 primary election.