NEW YORK (Reuters) - Front-runner Donald Trump showed signs of tightening his grip on the Republican U.S. presidential nomination on Wednesday when chief rival Ted Cruz acknowledged his own only hope of wresting control is a contested convention. Trump delivered a crushing defeat of Cruz in Tuesday’s New York Republican nominating contest while Democratic front-runner Hillary Clinton broke rival Bernie Sanders’ string of state victories with a definitive win of her own. Rebounding from a defeat in Wisconsin two weeks ago, Trump set himself up for another big night on April 26, when the Northeast U.S. states of Pennsylvania, Connecticut, Rhode Island, Delaware, and Maryland hold primaries. “Ted Cruz is mathematically out of winning the race,” Trump tweeted on Wednesday. “Now all he can do is be a spoiler, never a nice thing to do. I will beat Hillary!” Trump, 69, predicted some “amazing weeks” ahead for his campaign. Cruz, at a news conference on the sidelines of a Republican National Committee meeting in Hollywood, Florida, said neither he nor Trump will amass the 1,237 delegates needed to win the nomination without a contested convention in Cleveland starting on July 18. “What is clear today is that we are headed toward a contested convention. Nobody is able to reach 1,237. I’m not going to reach 1,237, and Donald Trump is not going to reach 1,237,” said Cruz, a U.S. senator from Texas. New York boosted Trump’s delegate tally to 845, while Cruz has 559 and Kasich 147, according to the Associated Press. Next Tuesday’s contests offer 172 delegates for Republicans.  CLINTON LEADS TRUMP -POLL If Trump, a New York billionaire, and Clinton, a former U.S. secretary of state, go on to secure their respective parties’ nominations, a Reuters/Ipsos national opinion poll shows Clinton with a sizeable lead if the Nov. 8 election were held today.   In the latest poll of likely general election voters, 45 percent said they would support Clinton while 35 percent would support Trump if the two were running against each other. The April 15-19 poll surveyed 1,334 people and had a credibility interval of 3.1 percentage points. A former reality TV star, Trump has adopted a more measured tone in recent days and appears to be trying to heal wounds inflicted by a campaign that has alarmed many in the Republican establishment. He sent campaign advisers to the party meeting in Florida that began on Wednesday. “There’s only two issues left for Republicans: Will Trump get 50 percent of the delegates prior to Cleveland, and if not, how close will he be? New York gives him a nice boost, but it will take weeks before we know the answer,” said Ari Fleischer, who was White House spokesman under President George W. Bush.  Cruz, 45, came in third in New York. Ohio Governor John Kasich, 63, a long-shot candidate, sought to use his second-place showing in New York as proof he is emerging as Trump’s central challenger. Trump won at least 89 delegates in New York, while Kasich got at least three, according to the AP. Cruz did not win any, prompting Trump adviser Sarah Huckabee Sanders to urge him on CNN on Wednesday to “get out of the way” once the math of delegate counts makes it impossible for him to prevail. The win by Clinton, 68, makes it nearly impossible for Sanders, 74, to overtake her commanding lead in delegates needed to secure the nomination. Clinton clinched at least 175 out of 291 New York delegates, while Sanders won at least 106, according to the AP. A U.S. senator from Vermont, Sanders has vowed to fight until the Democrats’ nominating convention in Philadelphia starting on July 25. Democratic strategist Jim Manley said Clinton has the delicate task of trying to attract Sanders supporters drawn to his leftist campaign promises, while switching focus to the task of beating the eventual Republican nominee. “She runs a risk. If she goes too far to the left she’s going to upset independents and others that she’s going to need in the general,” Manley said.    