Donald Trump's wife, Melania, took centre stage on the first day of the Republican National Convention but faced accusations that a portion of her speech plagiarised Michelle Obama.
Her speech, which brought the convention to its feet, had themes of inclusivity, honesty and hard work.
Commentators noticed similarities with Mrs Obama's 2008 convention speech.
But Mr Trump's team said Mrs Trump used "common words" and blamed Hillary Clinton for the row.
"There's no cribbing of Michelle Obama's speech," said Paul Manafort, Mr Trump's campaign manager.
"I mean, this is, once again, an example of when a woman threatens Hillary Clinton, how she seeks out to demean her and take her down,'' he added.
It was Mrs Trump's first speech of the campaign and she had the help of a speechwriting team.
Republican National Committee Chairman Reince Priebus he did not blame Mrs Trump, but added he would "probably" fire the speechwriter over the controversy.
Earlier, Mr Trump's communications adviser Jason Miller issued a statement saying a "team of writers" used her life's "inspirations" as source material.
Meanwhile Mr Trump himself described her speech as "absolutely incredible".
How the speeches compare
In a section, Mrs Trump said: "My parents impressed on me the values that you work hard for what you want in life; that your word is your bond and you do what you say and keep your promise; that you treat people with respect."
Mrs Obama's speech in 2008 carried the lines: "And Barack and I were raised with so many of the same values: that you work hard for what you want in life; that your word is your bond and you do what you say you're going to do; that you treat people with dignity and respect, even if you don't know them, and even if you don't agree with them."
Mrs Trump's speech continued: "[My parents] taught me to show the values and morals in my daily life. That is the lesson that I continue to pass along to our son. And we need to pass those lessons on to the many generations to follow, because we want our children in this nation to know that the only limit to your achievements is the strength of your dreams and your willingness to work for them."
Mrs Obama said: "And Barack Obama and I set out to build lives guided by these values, and pass them on to the next generations. Because we want our children, and all children in this nation, to know that the only limit to the height of your achievement is the reach of your dreams and your willingness to work for them."
The Slovenian-born former model had used the speech to portray her husband as a tough but compassionate unifying force.
"He's tough when he has to be but he's also kind and fair and caring," Mrs Trump said.
"The kindness is not always noted, but it's there for all to see. That is one reason I fell in love with him to begin with."
Mrs Trump has kept a lower profile compared with other spouses of major candidates. Her husband's adult children have often been more prominent.
Analysis - The BBC's Jasmine Coleman in Cleveland
It seemed to go so well for Melania Trump - she had delegates on their feet at the start and cheering wildly in approval by the end.
But hours later, as her words spread on social media, attention turned to the authenticity of her speech - and to the words of another aspiring First Lady.
What Republican delegates will make of the associations with Michelle and Barack Obama - so vehemently hated by so many Trump supporters - will undoubtedly feature in discussions over the coming days in Cleveland.
But then Trump's supporters are now so accustomed to defending their man from accusations in the media, they could still put this all down to another conspiracy against him.
Mrs Trump's mostly personal speech contrasted with the night's other speakers who spoke about "making America safe again".
Each day of the convention is based on a similar theme. Tuesday's focus will be "make America work again", with House Speaker Paul Ryan, UFC President Dana White and New Jersey Governor Chris Christie taking centre stage.
A wide range of speakers, including a county sheriff and a decorated combat veteran, told stories of military service, urban crime and the dangers of illegal immigration on Monday.
Former New York City Mayor Rudy Giuliani and Arkansas Senator Tom Cotton took aim at presumptive Democratic nominee State Hillary Clinton, questioning her judgement in foreign affairs.
"Who would trust Hillary Clinton to protect them?" said Mr Giuliani, whose rousing speech fired up the crowd at the Quicken Loans Arena in Cleveland, Ohio. "I wouldn't."
Many Republican party leaders - such as Ohio Governor John Kasich whose state is hosting the convention - have decided not to attend this year's festivities, turned off by Mr Trump's controversial stances on immigration and foreign policy.
Mr Trump has called for a ban on Muslims entering the US and also advocated deporting almost 11 million undocumented immigrants.
A speech by Wisconsin police sheriff David Clarke strongly defended police officers in the wake of the deadly shooting in Baton Rouge, which killed three officers over the weekend.
"Blue lives matter!" Mr Clarke said to huge cheers from the delegates in the convention hall.
The killings prompted Mr Trump to say the country was falling apart - a claim strongly disputed by President Barack Obama.
Earlier, anti-Trump delegates failed in their final push to block Mr Trump's nomination.
The vote that would have allowed delegates to back a candidate of their choice was quashed when three states reportedly backed out.
Some said the Republican Party officials had sabotaged their efforts on purpose.
The push was the last gasp for those who hope to see a different Republican candidate get the nomination.
A convention - all you need to know
1. What's the point? Each party formally nominates its candidates for president and vice president, and the party unveils its party platform, or manifesto.
2. Who is going? There are 2,472 delegates attending, selected at state and congressional district conventions, and representing each US state and territory. Plus 15,000 journalists and thousands of other party grandees, lawmakers and guests.
3. Who isn't going? Some senior figures who don't like Donald Trump have stayed away, including two ex-presidents named Bush, former nominee Mitt Romney and Ohio Governor John Kasich.
4. What's the schedule?
- Tuesday - House Speaker Paul Ryan, New Jersey Governor Chris Christie
- Wednesday - VP nominee Mike Pence
- Thursday - Donald Trump, introduced by daughter Ivanka