Republicans remained tense about the outcome, privately griping about Hyde-Smith, who was appointed to the seat in April, and a gaffe-filled campaign that has provided an opening to Espy.
Hyde-Smith appeared likely to coast to election after November 8, when she took 42 percent of the vote to Espy's 41 percent and Tea Party-aligned Chris McDaniel's (R) 17 percent in the all-party primary.
The race was marked by national attention directed at Hyde-Smith's remark this month complimenting a cattle rancher by saying, "If he invited me to a public hanging, I'd be on the front row".
Hyde-Smith has close ties to Donald Trump, who tweeted to congratulate her last night.
"We have worked very hard, and we feel very good", Hyde-Smith said.
Espy's campaign argued that Hyde-Smith's "toxic comments" were an embarrassment to MS and could scare away economic investments.
The video sparked a furor in the deep South state that has a history of racism and violence against blacks, including lynchings.
"Mississippians know me and they know my heart, and thank you for stepping up", she added.
In the wake of her remarks, several organizations, including Major League Baseball and Walmart, asked that their donations to Hyde-Smith's campaign be returned.
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Hyde-Smith's campaign hammered Espy for his $750,000 lobbying contract in 2011 with the Cocoa and Coffee Board of the Ivory Coast. Espy, who is black, called her comments "reprehensible".
Hyde-Smith and Espy faced off in the runoff after earning the most votes in the special election nonpartisan "jungle primary", which goes to a runoff when no candidate earns a majority of the votes.
Republicans even privately acknowledged that Hyde-Smith mangled her response to the video, and it wasn't until a debate last week that she offered a qualified apology.
The runoff was marked by racial acrimony over comments Hyde-Smith made. The state could soon have its first elected female senator or first black senator since Reconstruction. "She wasn't trying to send any messages".
The runoff contest drew comparisons to the Alabama Senate special election previous year, when Democrat Doug Jones won a narrow victory against Roy Moore, after the Republican faced multiple accusations from women that he had molested them when they were teenagers.
Her supporters said the furore over her comments was overblown.
Tuesday's victor will fill the last two years of the term of longtime Republican senator Thad Cochran, who resigned because of health problems, and have to run again in 2020.
"While this same-sex couple's request for a permit to utilize one of our state's facilities for a "commitment ceremony" is not being defined as a marriage ceremony, it is personally troubling for me", she said at the time, citing her "personal and religious beliefs". Thad Cochran stepped down due to health reasons, defeated former congressman and Agriculture Secretary Mike Espy. But if black voters rise to 40 percent of the electorate and Espy wins 9 out of 10, he needs less than a quarter of white votes for victory. "That really offended me", said Charles Connley, 60, a black voter from Picayune.