Saturday's race was shorn of a global superstar when Jamaica's Shelly-Ann Fraser-Pryce, the five-time world and two-time Olympic 100m champion, withdrew.
Yet Alfred delivered the star power at the Stade de France with a fantastic effort, as she cruised to victory in 10.72 seconds.
In the process, the 23-year-old claimed the first Olympic medal for Saint Lucia.
Alfred finished ahead of Sha'Carri Richardson, the reigning world champion.
Melissa Jefferson, Richardson's American compatriot, crossed in third, ahead of Great Britain's Daryll Neita.
Alfred, the Texas Longhorn senior who ran a NCAA record 22.01, the second fastest time ever indoors to win the NCAA Indoor Nationals last month, also established a new national record in the event that was contested over two heats.
Lenae Thomas also of Texas was second overall in a wind-aided 22.30 (+3.1m/s) that won the second heat.
MacKenzie Long of Ole Miss, second in Alfred’s heat, was third overall in 22.31. Kevona Davis, who was third in Alfred’s heat ran 22.47 for fifth overall.
In the Women Olympic Development 200m, World Championship 100m bronze medallist Elaine Thompson-Herah, running her first 200m of the season, finished in second place in her heat in 23.23, a time good enough for second overall.
Melissa Jefferson of the USA, who won Thompson-Herah’s heat, was the fastest with a time of 23.02.
In a stunning display of speed and determination, Alfred crossed the finish line first, and, much like she did when she copped the World Indoor title earlier this year, etched her name into the annals of Olympic history, bringing immense pride to her island nation.
On a cool, and wet evening at the Stade de France, Alfred, running from lane six, delivered a performance that will be remembered for generations. The 23-year-old’s explosive start and powerful finish left competitors in her wake, as she clocked a National Record of 10.72s in a negative 0.1 metres per second wind reading.
After crossing the line, Alfred raised her arms in triumph but later burst into tears, overwhelmed by the magnitude of her achievement. She is now the third Caribbean sprinter to win the title after Jamaicans Shelly-Ann Fraser-Pryce and Elaine Thompson-Herah, but more importantly, Alfred also ensured that the women's 100m gold goes to a Caribbean representative for a fifth Olympic Games.
The American duo of Sha’Carri Richardson (10.87s) and Melissa Jefferson (10.92s) took silver and bronze. Jamaica’s Tia Clayton (11.04s) had a slight stumble early and was left back in seventh.
In what is her final Olympic Games, Fraser-Pryce, who boasts a rich legacy as one of, if not the greatest female sprinter of all time, was expected to end this chapter of her career on a high. However, after arriving in the call room, the 37-year-old, who has had her struggles with injuries this season, was later seen heading back to the warm-up area, and news of her withdrawal sent ripples through the track and field community.
While Fraser-Pryce’s competitors' respect and admiration for her is evident, they had to focus on their own task at hand in the hunt for Olympic glory.
In her absence, St Lucia’s stalwart Alfred finished tops in semi-final two, as she got away well from lane six and was not for catching. She won in 10.84s, ahead of American World Champion Sha’Carri Richardson (10.89s), who closed late.
Jamaica’s rising sensation Tia Clayton, now viewed by many as a proverbial ‘dark horse’ in the event, won semi-final three in 10.89s, pulling Great Britain’s Daryll Neita (10.97s) with her. American Twanisha Terry (11.07s) was third and progressed as one of the fastest non-automatic qualifiers. Trinidad and Tobago's Leah Bertrand (11.37s) was ninth.
Earlier, American Melissa Jefferson topped semi-final one in 10.99s, with Ivory Coast’s Marie-Josee Ta Lou-Smith (11.01s) closing fast to take the second automatic qualifying spot. Switzerland’s Mujinga Kambundji (11.05s) got the other non-automatic qualifying spot.
Jamaica’s Shashalee Forbes (11.20s) was sixth.
The final is scheduled for 2:20pm Jamaica time.
Richardson's final at Hayward Field started with an intense stare-down, a marked departure from her exuberant salutes to the crowd in earlier heats. This newfound focus paid off spectacularly, as Richardson blazed down the track to clinch victory and her first Olympic berth.
Joining her on the plane to Paris are training partners Melissa Jefferson and Twanisha Terry, who finished second and third with times of 10.80 and 10.89 seconds, respectively. Jefferson's time was a lifetime best.
This victory marks a significant milestone in Richardson's career, especially after the disappointment of missing the Tokyo Olympics due to a suspension for marijuana use. She acknowledged the struggles she has faced, saying, "Everything I've been through is everything I have been through to be in this moment right now. There's nothing I've been through that hasn't designed me to sit right here in front of you to answer this question."
Richardson's resurgence has been marked by notable achievements, including winning the 100m at the world championships in Budapest last summer with a personal best of 10.65 seconds. She also anchored the US 4x100 relay team to victory.
Richardson's next goal is to qualify for the 200m. She enters the event with the third-fastest qualifying time, behind Tokyo Olympic bronze medalist Gabby Thomas and 2024 NCAA champion McKenzie Long. The first-round heats for the women's 200m are scheduled for Thursday.
Before Richardson's electrifying performance, Noah Lyles, the reigning world champion at 100m, ran his preliminary heat in 9.92 seconds, the fastest time in the first round of men's qualifying. Christian Coleman also advanced winning his heat in 9.99 while Fred Kerley ran 10.02 to also advance.
