Hernych started his professional career in 1998 and set the first accents with two ITF tournament victories. In 1999 he defeated his first top 100 player with the Spaniard Albert Portas . Two years later he celebrated his first Challenger success in Tulsa , Oklahoma : He won the final against Vincent Spadea 7-5, 7-5.
In 2004 he won his second Challenger tournament in Prague and took part in tournaments on the ATP World Tour for the first time. He achieved several prestigious victories, including against the then world number 12 Mark Philippoussis and the Brazilian Gustavo Kuerten . He also played at Wimbledon , but was eliminated in the first round. In August 2004, Hernych was for the first time among the top 100 in the world rankings .
The following year he consolidated his top 100 position and defended his title in Prague. In addition, he moved into the second round of three of the four Grand Slam tournaments, only the US Open he finished in the opening round. In April 2006 he defeated the then number six Nikolai Dawydenko 7: 5, 7: 5 in Valencia , which was his only win to date against a top 10 player. Two months later he celebrated another premiere with the final of the ATP tournament in 's-Hertogenbosch , but lost to Mario Ančić in three sets.
On April 27, 2009, Hernych reached 59th place, his best world ranking so far. His greatest achievement is reaching the third round of the 2011 Australian Open . As a qualifier in the first round, he won 6: 3, 6: 4, 3: 6, 6: 2 against Denis Istomin . The following game against Thomaz Bellucci developed into a marathon game: only after 4 hours and 36 minutes did Hernych convert his match point to 6: 2, 6: 7 (11:13), 6: 4, 6: 7 (3: 7) , 8: 6. In the third round he finally lost significantly to Robin Söderling .
Double
Since 1998, Hernych has been regularly represented in doubles tournaments. In 2002 he celebrated his first Challenger tournament victory at the side of Shaun Rudman in Wolfsburg , a year later he was successful together with Uros Vico in Aptos . In 2009, as a double partner of Ivo Minář, he won the ATP tournament in Munich with a 6: 4, 6: 4 against the then top 30 players Ashley Fisher and Jordan Kerr .
Hernych played his last professional tournament in February 2018, where he failed in the first round of qualification to João Souza .