Novak Djokovic turned professional in 2003.
Djokovic began his professional career as a teenager, playing his first professional match in January 2003 at a Futures event in Oberschleißheim, Germany. He lost narrowly to Alex Rădulescu, but later that year won his first Futures title in Belgrade and finished the season ranked world No. 687.
His rise continued quickly. In 2004, he earned his first ATP-level victory during a Davis Cup match and won his first Challenger title in Budapest on his 17th birthday. He made his ATP Tour main-draw debut at the 2004 Croatia Open in Umag, then entered the Grand Slam stage at the 2005 Australian Open.
The year 2003 marks his professional beginning, not his first major championship or his breakthrough into the sport’s elite. Djokovic won his first Grand Slam title at the 2008 Australian Open, aged 20. He later became one of the defining players of the era alongside Roger Federer and Rafael Nadal.