In the first showdown between Hillary Clinton and Donald J. Trump, the presidential candidates exchanged blows on trade and foreign policy, called each other racist and inept, and could not resist letting out stray smirks or occasional sniffles.

Commentators across the web on Monday night tended to conclude that their favored candidate had come out on top. But on balance, Mrs. Clinton was seen as having had the better night, based on the contrast between her steady grasp of policy and Mr. Trump’s tendency to ramble and occasionally raise his voice.

Here is a sample of reaction on social media and elsewhere online:

“Clinton was in command from beginning, succeeded where Trump’s GOP opponents failed: remain unflappable and in control of arguments. No knockout blow but Clinton won this debate hands down. Trump struggled with format, duration, and facts and rambled.”

Kim Ghattas, BBC correspondent

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“Great that debate covered Trump’s taxes, income, father, ’72 lawsuit, remarks as a reality TV star and didn’t waste any time on immigration.”