Cheptai began to make an impact at senior level in the 2013 season, starting with a runner-up finish at the Cross Internacional de Itálica and third place at the Cross Internacional Juan Muguerza. Second place to Margaret Muriuki at the Kenya Cross Country Championships brought on her selection for the senior national team, and finished tenth at the 2013 IAAF World Cross Country Championships (although only fifth best among the winning Kenyan team). She competed on the IAAF Diamond League track circuit for the first time that year and managed personal bests of 8:56.20 minutes and 14:50.99 minutes for the 3000 m and 5000 m.