Washington: Republican Donald Trump had another great night with three major victories and a near tie, while a big loss in his home state of Florida prompted Marco Rubio to drop his White House bid.
Democratic frontrunner Hillary Clinton too scored major wins in Florida and North Carolina and in a crucial victory, she stopped self-styled Democratic Socialist rival Bernie Sanders in his tracks in the industrial Midwest by taking Ohio.
Trump won Republican primary victories in Florida, North Carolina and Illinois and was in a virtual tie with closest rival Ted Cruz in Missouri getting at least 159 more delegates and taking his total to 619 from 18 wins.
However, his loss in Ohio to its Governor, John Kasich made it more difficult for the brash billionaire to reach the 1,237 delegates he needs to capture the Republican nomination without a heated contest. Cruz has 394 delegates, Rubio 167 and Kasich 136.
But Trump's victory in the biggest contest of the night, taking all off Florida's 99 delegates forced Rubio out of the race and upended Republican establishment's plans to get united against the real estate tycoon.
"This was a great evening," he said in his primary night address describing himself proudly as a candidate of the angry and disaffected.
"There is great anger," Trump said. "Believe me, there is great anger."
"We have to bring our party together," he said urging party unity amid growing speculation about the potential of a convention fight. "We have to bring it together."
Conceding defeat, Rubio warned that Trump's politics of division will leave America a "fractured nation".
"America is in the middle of a real political storm, a real tsunami and we should have seen this coming," he said. "While we are on the right side," he said, "this year, we will not be on the winning side."
Trump on the other hand congratulated the Florida senator "for having run a tough campaign".
"He is tough," Trump said. "He is smart and he has got a great future."
On the Democratic side, Clinton won the Florida and Ohio primaries and with a win in North Carolina completed her sweep of Southern states where she has enjoyed strong support from African-American voters.
"We are moving closer to securing the Democratic Party nomination and winning this election in November," Clinton said in a victory speech in West Palm Beach, Florida.
She said that by the end of the night she would have two million more votes than Sanders, and hold a lead of more than 300 in the delegate count.
Even in defeat, Sanders delivered his standard campaign speech, decrying the influence of big money in politics and vowed that "billionaires would have to pay their fair share".
Describing "Rubio's demise" as "the last gasp of the Republican reboot", the Washington Post said "Years of carefully laid plans to repackage the Republican Party's traditional ideas for a fast-changing country came crashing down" with him quitting the race.
The New York Times said Rubio's exit had "spoiled the Republican buffet". Kasich, it suggested, "is the best of the remaining three candidates, but has little to no chance of pulling past either of the other two in the delegate count.
"Those two, Donald Trump and Ted Cruz, are merely different flavours of rancid fare," said the influential daily which has endorsed Kasich and Clinton for their parties' nominations.