text: Cassells, 22, and Scrimgeour clocked six minutes and 29.63 seconds to finish ahead of Denmark and China.
  The British duo won the title in the non-Olympic class in France last year.
  Meanwhile Ireland's Olympic silver medallist Paul O'Donovan, 22, won his lightweight single sculls semi-final.
  The Skibbereen man, who clinched Olympic silver in the lightweight double sculls in Rio with his brother Gary, produced a strong late burst to come from fourth at the halfway stage to win his semi-final in 6:51.71.
  Slovenian Rajko Hrvat finished second in 6:52.31 with Germany's Konstantin Steinhuebel clinching the third qualifying spot for Saturday's final.
  The Rotterdam championships features non-Olympic classes.
  Irish duo Mark O'Donovan and Shane O'Driscoll will compete against Cassells and Scrimgeour in Saturday's lightweight pairs final after finishing second in their semi-final behind the French boat.
  The British pair were the fastest qualifiers for final, ahead of the Danes (6:30.12) and France (6:30.56), while the Irish duo next quickest in 6:32.18.
  After winning gold in their class at last year's World Championships in France, Cassells and Scrimgeour retained the European title in Brandenburg in May.
target: Coleraine rower Joel Cassells and Great Britain team-mate Sam Scrimgeour remain on course to defend their lightweight pairs world title after winning their semi-final in Rotterdam on Thursday.