Houston, TX, USA, 10 April 2014 | AAP

Lleyton Hewitt has been knocked out of the US men’s clay court championships in Houston, going down to American Sam Querrey in the second round.

Querrey beat the 2009 champion and Australian veteran 6-3 6-4 on Wednesday to book a spot in the quarterfinals.

The 2010 finalist will next face either top-seeded countryman John Isner or Germany’s Dustin Brown.

Former world No.1 Hewitt made a promising start to the tournament, toppling Canadian Peter Polanksy in their first-round clash on Tuesday.

Hewitt’s compatriot Matthew Ebden also had his campaign cut short, falling 6-1 6-2 to Colombian Santiago Giraldo in just 57 minutes in their opening match of the tournament.

Meanwhile sixth-seeded Argentine Juan Monaco, the 2012 champion, became the fifth active player to 200 match wins on clay thanks to his first-round victory over Somdev Devvarman.