In August 2008 Van der Merwe also reached his first Challenger tour final at the Campos Do Jordao-1 in Brazil, where he lost to Brian Dabul.

In August 2010 Van der Merwe won his maiden ATP Challenger title at the Campos Do Jordao-1 in Brazil, when he defeated world number 88 Ricardo Mello.

In April Van der Merwe won his second ATP Challenger title at the Soweto Open in Johannesburg, South Africa, when he defeated countryman and world number 184 Rik De Voest.

In November Van der Merwe won his third ATP Challenger title at Charlottesville, Virginia, United States, when he defeated world number 283 Jesse Levine.

In July he reached the quarterfinal of the Hall of Fame Tennis Championships (ATP 250 event) in Newport, RI, U.S.A. .