Stefan Kozlov (/ˈstɛfɑːn ˈkɒzlɒv/ STEF-ahn KOZ-lov; born 1 February 1998) is an American professional tennis player of Russian descent. He is the son of Russian parents and his father is a tennis coach.
Kozlov made his ATP World Tour debut as a wild card in Newport at the age of 15. He reached two junior Grand Slam finals in 2014 and finished the year at No. 3 in the ITF Junior Combined rankings.
In 2014, Kozlov reached two junior grand slam finals, where he lost to Alexander Zverev at the Australian Open and Noah Rubin at Wimbledon. This success led him to a career high junior ranking of No. 2. Kozlov also competed at the U18 National Championships, finishing in third place in the singles tournament and winning the doubles tournament with Noah Rubin. With this victory, they earned a wild card into the main draw of the 2014 US Open. He ended the year by winning the Orange Bowl junior tournament.