Hambüchen's first major senior competition was the 2003 World Artistic Gymnastics Championships in Anaheim. He competed 4 events in qualifications but the German team did not advance to the team final.

Hambüchen was the youngest German athlete at the 2004 Summer Olympics in Athens where the German team placed 8th in the Team Final. Individually, Hambüchen finished 23rd in the All Around and seventh in the horizontal bar final.

in 2005, Hambüchen won the horizontal bars title at the 2005 European Artistic Gymnastics Championships. At the 2005 World Artistic Gymnastics Championships, Hambüchen competed 3 events in qualifications and placed 4th in the horizontal bar final.

Hambüchen competed at the 2006 European Artistic Gymnastics Championships where the German Team placed 7th. Individually, 2005 Euuropean Artistic Gymnastics Championships placed 5th in the vault final and 7th in the parallel bars final.

At the 2006 World Artistic Gymnastics Championships, Hambüchen won his first World Championship medal at the age of 18 with bronze in the All Around. He also won a bronze on vault despite having the lowest combined difficulty in the final. The German Team placed 7th in the Team Final, with Hambüchen contributing scores on 5 events. However, Hambüchen did not qualify to the horizontal bar final.

In 2007, Hambüchen competed at the 2006 European Artistic Gymnastics Championships where he won the silver medal in the All Around, and won the European horizontal bar title for the second time.

...
Wikipedia