The other two Republicans in the race, Marco Rubio and John Kasich, had poor performances, with Rubio's hopes of being the establishment alternative to Trump now lying in tatters. A loss in Florida, his home state, which votes next week, will effectively end his campaign, although a win in Puerto Rico had him talking up his chances yesterday.
Cruz, a senator from Texas, heaped pressure on Kasich and Rubio to abandon the race. "I'm having conversations from all sorts of people and we're seeing supporters of other candidates come joining us," he said.
"They're recognising that their candidates were not in a position to beat Donald."
Cruz added 64 delegates to his tally on Sunday, while Trump gained 49. Trump now has 378 delegates to Cruz's 295 as he tries to reach the winning 1237 tally that would remove the establishment's chance of taking the race to a contested convention and nominating an alternative candidate.
Trump, in his victory speech in Florida on Sunday, declared himself primed for a head-on contest with Cruz.
"I would like to take on Ted one-on-one," Trump said, ticking off a list of big states where he believed Cruz had no chance.
But Cruz, spearheading the Stop Trump campaign, said it was essential for the very soul of America that the billionaire businessman was defeated.
"Think about what presidents have meant in history," he said. "Think of Lincoln's Gettysburg Address. Think of FDR saying, 'The only thing we have to fear is fear itself'.
"I think people are asking themselves, 'How would we feel if our children came in repeating the words of the president of the United States if that president was Donald Trump'."
Thevoting continues for the Republicans today in Mississippi, Idaho and Hawaii, and in Michigan for the Democrats.
