The southpaw boxed as an amateur for the Boxabteilung of SV Halle and won 122 fights with 19 defeats and three draws. His first international success was winning the European Championship in the age class of the Cadet (U -17) in the light heavyweight division in 1996 in Aosta. In 1997, he took second place at the Junior European Championships in Birmingham.
Meanwhile in the heavyweight boxing, he started as German representative at the Junior World Cup in 1998 in Buenos Aires. After a points victory over the Italians Roberto Cammarelle, he met in the quarterfinals on the later Olympic champion Odlanier Solís in 2004 and lost to the Cubans 1:8 on points.
After the change to the seniors in 1999 he took part in the Amateur World Championship in Houston and was able to advance to the semi-finals there. His opponent in this encounter was the American Michael Bennett. However Kretschmann sprained in battle when attempting to hook up the hand, was forced to retire due to injury then after the second round and finished the World Cup thus in third place from.
1999, 2001 and 2002, Kretschmann was German heavyweight champion. In 2002, he defeated it in the final Dieter Roth.
At the World Championship 2003 in Bangkok, he took a third place again, he lost in the semifinals prematurely against Russian Alexander Alexeyev. In 2004 he became the Superschwergewichtler at the Military World Championship in Fort Huachuca of place in the final against the Italians Cammarelle, but had then an injury without a fight settle for second place.
In chemistry Cup, he finished in 2002 with a semi-final defeat against Sultan Ibragimov third place. In 2005, the tournament for Kretschmann ended in the semifinals with a first-round KO by the Cuban Michel Lopez.
Kretschmann was in Germany for many years as a competitor of 2006 also turned professional exchanged Sebastian Köber.
- German Champion 1999, 2001, 2002 ( heavyweight)
- European Champion - 1996 Cadets, Juniors 1997 ( light heavyweight )
- World Cup - Third 1999, 2003 ( heavyweight)
- Military World Championship - Second 2004 ( super heavyweight )
In October 2006, Kretschmann signed a professional contract with the Hamburg boxing stable Arena Box-Promotion and gave on 10 November 2006 his successful pro debut. After he won his first 13 fights against construction opponent, he was supposed to start on 6 March 2009 against Denis Bakhtov, the reigning heavyweight champion of the Pan Asian Boxing Association (PABA ), but the fight had to because of a suffered in training eardrum rupture, which required surgery first cancel. The fight against Bakhtov was then postponed to 26 June 2009 Völklingen and Kretschmann defeated the Russians technical knockout in the first round. On March 27, 2010, there was in the Sporthalle Hamburg for rematch against Bakhtov, the Kretschmann gave in the lead in the ninth round.
On September 14, 2012, he boxed against Timo Hoffmann; However, the fight ended wertungslos in the sixth round, since the onset of rain prevented a continuation of the outdoor event.