WASHINGTON - Preparation matters. That's the simple takeaway after the highly anticipated first presidential debate between Democratic nominee Hillary Clinton and her Republican rival Donald Trump at Hofstra University in New York.

Mrs Clinton had spent much of the preceding weeks rigorously studying her opponent's positions and even building a mock stage and staging practice debates at night to make sure she was used to the process.

Mr Trump, in contrast, said there was such a thing as being too prepared and wanted to make sure he did not sound too rehearsed.

The result was a debate that Mrs Clinton largely dominated, scoring the better lines, showing a better mastery of the issues and successfully getting under Mr Trump's skin on issues like his business dealings, and his attitudes towards minorities and women.

The former secretary of state, who has also had more real one-on-one debate experience, continually put the tycoon on the defensive, baiting him into ill-advised answers on a range of issues.

When she accused him of not paying any federal income tax, Mr Trump interrupted her and proclaimed: "That makes me smart!"

And when she talked about how Mr Trump had received a US$14 million loan from his father to start his business, the businessman retorted that he received a "very small loan".

Later, in a segment on race relations when Mrs Clinton brought up a 1973 lawsuit against Mr Trump for discriminating against African-American tenants, the billionaire issued this curious non-denial: "We settled the suit with zero - with no admission of guilt. It was very easy to do."

He interrupted Mrs Clinton repeatedly during the debate and argued with moderator Lester Holt.

But perhaps the two most damaging moments of the night came on the issues of President Barack Obama's birthplace and the question of temperament.

The fact that the question of Mr Obama's birthplace would come up was no surprise to Mr Trump - and he said so himself - given that he has long questioned if the President was born in the US. Yet, he failed to adequately answer the question of why he recently conceded that Mr Obama was in fact born in the US.

He went on about it in a prolonged answer that included debunked claims that Mrs Clinton's campaign started the rumour and he ended it, an attempt to talk about other issues and then saying he had a good relationship with the African-American community.

After the long answer, Mrs Clinton produced a line that drew laughter from the audience: "Well, just listen to what you heard."

The second damaging moment was when Mr Trump tried to defend his temperament. Coming in to the debate, one of the tycoon's major aims was to convince Americans that he had the temperament to be president. And for the large part of the debate, Mr Trump was more restrained than during the primary debates. He even decided to call Mrs Clinton "Secretary Clinton", while she opted to call him "Donald" throughout the debate.

But close to the end of the session, when Mr Trump said "I also have a much better temperament than she has", the audience could be heard laughing - a bad sign for any candidate.

Even when there were clear opportunities for attack - like when Mrs Clinton's e-mail scandal came up - Mr Trump failed to make the most of them, possibly because he did not have a good enough grasp of the facts to really push the point.

He started on a promising line of attack about how Mrs Clinton's e-mail scandal was not a mistake but an intentional act, but then quickly moved on to defend an attack about his tax returns.

What positive moments there were for Mr Trump all came in the earliest part of the debate. He appeared presidential then and stuck to his two core messages: His business acumen is what the country needs, and the same old politicians have been ineffective.

Mr Trump, however, strayed from the messages as the debate wore on. He clearly also had the stronger position on the issue of free trade and the Trans-Pacific Partnership free trade deal, which is currently politically unpopular in the US.

On her part, Mrs Clinton appeared studied and calm, although it is unlikely she would have done much to sway those who either are angry with establishment politicians or do not consider her trustworthy.

Foreign policy and Asia featured relatively lightly in the 90-minute exchange. China came in for the usual attacks when discussions of free trade came up and Mrs Clinton pointed out that Mr Trump was in favour of Korea and Japan having nuclear weapons but neither issue was heavily discussed.

Though most experts agree that Mrs Clinton won the night on substance, there is an important caveat to the whole thing. This is not the first time experts have declared Mr Trump a loser at the debates only for him to emerge unscathed.

The billionaire has displayed a remarkable resilience to gaffes and blunders that would bury any other candidate and it may well happen again.

Despite the many little victories, there was certainly no knockout blow for Mrs Clinton and polls are unlikely to see much swings before the two meet again on Oct 9.

If the narrative coming in to the debate was that Mrs Clinton holds an edge in a close race, that will almost certainly be true after it.