Klobucnik qualified for the men's 200 m breaststroke at the 2012 Summer Olympics in London, by breaking a long-course Slovak record, eclipsing the FINA B-cut time of 2:13.10 at the European Championships in Debrecen, Hungary. He challenged seven other swimmers in the second heat, including four-time OIympian Jakob Jóhann Sveinsson of Iceland. He raced to third place by less than 0.11 of a second behind Poland's Slawomir Kuczko in 2:13.40. Klobucnik failed to advance into the semifinals, as he placed twenty-third overall in the preliminaries.