RIO DE JANEIRO — Jemima Jelagat Sumgong became the first Kenyan to win the women’s Olympic marathon Sunday after a scary moment near the finish when police intercepted a man who nearly marred the event.  Sumgong completed the course in 2 hours 24 minutes 4 seconds, giving Kenya its first gold medal in Rio.  The Kenyan-born Eunice Jepkirui Kirwa, who runs for Bahrain, was nine seconds behind and the world champion Mare Dibaba of Ethiopia took bronze.  With about a kilometer to go to the finish line at the Sambódromo parade grounds, a man with a sign jumped over barriers along the route ahead of Sumgong and the other runners, and two police officers on bicycles immediately cut him off. The protester then jumped over fencing on the left side of the road, and Sumgong and the other runners continued unhindered.  Sumgong said she was scared at first, worried that the man might “grab one of my colleagues.”  When Sumgong, 31, ran the London Marathon in April, a man tried to intercept her there. But her outcome was the same: victory.  “I was never worried that I’d lose this,” Sumgong said. “At 40 kilometers, I knew the gold was mine. At 35 kilometers, I noticed that my other two teammates had dropped off, and that gave me the motivation to carry on.  Sam Manchester will guide you through the 2016 summer Olympics in Rio de Janeiro.  Hey. It’s Sam from the NYT Sports desk. I’m at the Olympics in Rio (so you don’t have to be :)). Grab a limited spot and I’ll text you updates, answer your questions and share the behind-the-scenes stuff nobody else gets.  Thanks! Talk to you soon.  U.S. numbers only. Standard messaging rates may apply. Your information is used only to deliver messages about the Rio 2016 Olympics.  “At 40 kilometers, I saw there were three of us, but I knew whatever happened, I couldn’t lose the gold, and then I knew I was on the way to history.”  The breakaway began with about seven kilometers to go.  “It was very hot, but everybody had to get through the heat,” Sumgong said. “I had to control my body and listen to my body very carefully.”  Sumgong is only the third Kenyan woman to become an Olympic champion, following wins on the track at the 2008 Beijing Games for Pamela Jelimo (800 meters) and Nancy Jebet Langat (1,500 meters).  Only two of the Estonian triplets in the marathon completed the race. Lily Luik was the fastest of the 30-year-old sisters, clocking 2:48:29 to finish in 97th place.  Leila Luik ended up in 114th place in 2:54:38. But Liina Luik didn’t finish, withdrawing before the 35-kilometer mark.  “It was so hard,” Lily said. “I saw everybody stopping, and everybody suffered.”  One of the favorites left the race prematurely. Tigist Tufa, the 2015 London Marathon champion, pulled up after 18 kilometers.  A version of this article appears in print on August 15, 2016, on page D6 of the New York edition with the headline: Marathon Leader Hangs On After Interloper Is Thwarted. Order Reprints| Today's Paper|Subscribe
Jemima Jelagat Sumgong, who became the first woman from her country to win the Olympic marathon, ran unhindered while the police intercepted an intruder.