Born in Brno, Blažek started his career in Slavia Prague, where he got to play his first league games. After two years during which he was mainly used as a substitute, he moved to Dynamo České Budějovice to become the number one goalkeeper there. This season was to be the last of the Czechoslovak First League, and he decided to spend his first season in the new Gambrinus liga with Viktoria Žižkov, which turned out to be a good choice since he won his first title, the national cup. He left after only one year though, returning to Prague, this time to FC Bohemians. They were relegated that year and Blažek, who did not want to spend a year in the Druhá liga, was loaned for one year to his first club Slavia Prague, where again he was but a substitute. Since Bohemians regained promotion the same year, he returned there and stayed for three and a half years. However, while his club was not performing very well, Blažek drew the attention of giants Sparta Prague, transferring there in early 2000 and winning back-to-back titles in 2000 and 2001. He went on loan to rivals Marila Příbramin 2001 but returned after one year. After that, he played almost every single game for Sparta Prague, be it league, cup or Champions League games. It was a very successful period for Blažek as he won four more titles and three national cups. In 2007, he decided to try a first experience abroad and was sold to German club 1. FC Nürnberg, who purchased him as a replacement for Raphael Schäfer who had left for VfB Stuttgart over the summer. Blažek was the number one there but fell sick in April and could not play the end of a season that saw Nürnberg being relegated. In June, it was announced that Blažek was returning to Sparta Prague for the following season. However, on 16 December 2011, Sparta Prague announced their decision to terminate Blažek's contract early, releasing him as a free agent. This was confirmed by the player's agent Pavel Paska. On 22 February 2014, in a league match for Jihlava against Znojmo, Blažek kept his 139th clean sheet, setting a new goalkeeper record for the Czech league.
International career
Blažek made his debut for the national team on 29 March 2000 in a friendly against Australia that ended up in a 3–1 win. He was however never able to be but the number two behind Petr Čech. He was part of the Czech roster at both Euro 2000 and Euro 2004, but only played in one match during the two tournaments combined. He was also on the Czech roster for the 2006 World Cup.
