In the senior category Nyisztor posted a quarter-finals finish at the 2001 European Championships in Koblenz after he lost to Russia's Pavel Kolobkov, then another at the 2002 edition, losing this time to Hungary's Gábor Boczkó. Nyisztor climbed his first World Cup podium with a bronze medal at the 2003 Bratislava Grand Prix, but he could not attend the 2003 World Championships because the Romanian Fencing Federation was late for registration. He however qualified to the individual event at the 2004 Summer Olympics through the European zone qualifier in Ghent, becoming the first male épée fencer to represent Romania at Olympic Games. For his Olympic début he defeated Ukraine's Bohdan Nikishyn in the preliminary round, but lost to Italy's Alfredo Rota in the table of 32.