At the European Youth Chess Championship, held in Herceg Novi in 2005, Viktor was a bronze-medallist in the under-18 category.

Viktor was successful in Brno in both 2005 and 2006, the latter when he won the full national Czech Championship. This was also the year that he qualified as a GM and started his Olympiad career, scoring the best individual result of the Czech team in Turin.

In 2007, he was joint winner of the Czech Open (with Vlastimil Babula), held in his home town. He qualified for the Chess World Cup 2007.

In 2008, he shared victory with Krishnan Sasikiran at Calcutta and was declared winner on tie-break. He then took a share of second place at the EU Individual Open in Liverpool, behind Jan Werle (and equal with Michael Adams and Nigel Short).

In July 2010, he took clear first place at the World Open Chess Tournament with 7½/9.