On 24 January 2003, Kotelnik won his first regional championship—the vacant WBA Inter-Continental light-welterweight title—following a unanimous decision (UD) over Fabrice Colombel.

[3] Almost exactly a year later, on 22 March 2008, Kotelnik won the aforementioned WBA world title—now held by Gavin Rees—by stopping the champion in the twelfth and final round.

[4] Two successful defences were made: a UD against Norio Kimura on 13 September 2008,[5] and a close SD against future world champion Marcos Maidana on 7 February 2009.

[7] After more than a year of inactivity, he returned on 7 August 2010 to face unified WBC and IBF light-welterweight champion Devon Alexander, but lost a UD which was widely viewed as controversial and a "robbery".

[8][9][10] Having spent more than four years out of the sport, Kotelnik had a farewell fight on 4 October 2014, winning a dominant eight-round UD over Alexander Benidze.