He is noted for his backhand, which he cites as his best shot. His favorite surface is hard courts. Illya began playing tennis at age seven. His father Vassili and mother Anna are both engineers. Has one older brother, Igor Marchenko, a manager and former ice skater who took part in the 1998 Winter Olympics. Growing up, he admired Lleyton Hewitt and Roger Federer. He has played doubles on the Futures level with fellow Ukrainian Artem Smirnov. He was coached by Orest Tereschuk from July 2009 till 2014 and by Tibor Toth from 2014. Marchenko also has a YouTube channel with close to 3,000 subscribers and 150,000 views where he posts tennis-related content.
Yosuke Watanuki (綿貫 陽介, Watanuki Yōsuke, born 12 April 1998) is a Japanese tennis player. On the junior tour, Watanuki has a career high combined ranking of 2 achieved on 21 March 2016. Watanuki was the winner of the 2016 Campeonato Internacional Juvenil de Tenis de Porto Alegre, a Grade A event in Porto Alegre, Brazil. His first match victory on the 2018 ATP World Tour came at the 2018 Rakuten Japan Open.