Diana Kipyokei of Kenya wins the women’s race of the Boston Marathon.

Diana Kipyokei of Kenya won the Boston Marathon on Monday in her major marathon debut. At 27, her previous biggest victory was the Istanbul Marathon.

The race began in a typical pattern, with a large lead group forming and runners gradually dropping away. The pack was still 20 strong by the halfway mark. The race didn’t really begin until 18 miles in, when Kipyokei surged ahead.

Netsanet Gudeta of Ethiopia, a former world cross-country champion, went after her and caught her within a few miles. Sometimes when a lone leader is caught in a marathon, it’s the end of the line for her. But at 24 miles, after the two had run side by side, it was Kipyokei who again took the lead.

The veteran Edna Kiplagat of Kenya, a pre-race favorite and a two-time world champion as well as a New York and Boston winner, soon caught Gudeta and gave chase to Kipyokei. She gained some time but could not close the whole gap.

Kipyokei finished her unexpected victory, in a field with many more accomplished runners, in 2 hours 24 minutes 45 seconds. Kiplagat, 41, finished second in 2:25:09. Kenyans took the top four spots, with Mary Ngugi third and Monicah Ngige fourth. Nell Rojas was the top American in sixth.