Right after the Croatian event, Džumhur went to Dominican Republic, where he dominated the first edition of 2015 Milex Open, played on green clay in Santo Domingo, and became the first player who has ever won a professional tennis tournament in that country. Džumhur did not lose a set on his way to the title and spent on court less than five and a half hours in total during whole tournament week. He won the final against Renzo Olivo by retirement. It followed wins over Benjamin Balleret, Bastian Trinker, Nicolas Jarry and Christian Garin. Džumhur was then accepted to the main draw of 2015 Morelos Open, as a special exempt, where he managed to win further four matches, bringing his tally to nine wins in a row, and thus reaching the second consecutive final on Challenger level, and his career-first played on hard surface. He lost to Víctor Estrella Burgos, but his semifinal win against Adrián Menéndez-Maceiras, where he saved two match points, gave him first ever placement inside the top 100 in ATP rankings, which made Džumhur the first male representative of Bosnia and Herzegovina to do so, and also the highest ranked player in a singles ranking list competing under the Bosnian flag (surpassing Mervana Jugic-Salkić's No. 99 ranking from June 2004).
