Achterberg first signed for Tranmere Rovers in 1998, after a successful trial as a replacement for the Everton bound Steve Simonsen. He was immediately selected for the first team due to an injury to Danny Coyne, making his debut against Swindon Town on 25 September 1998. Achterberg then secured his place as Rovers' first choice goalkeeper after Coyne was transferred to Grimsby Town in 1999. Achterberg became part of the giant-killing cup teams that defeated such opponents as Everton, Southampton and other big teams. However after refusing to sign a new contract he was dropped by John Aldridge for the 2000 Football League Cup Final and replaced by Joe Murphy. Achterberg's proficiency in goal was exemplified by the 20 clean sheets he kept during the 2003–04 season under the stewardship of Brian Little. One of his more memorable performances was against Millwall in an FA Cup quarter final at The New Den which was televised on BBC 1. The game finished goalless, but was largely dominated by Millwall and John managed to save a penalty kick from Kevin Muscat, despite having to play through injury.