Former European Open winner Ferrie, who at 110th in The Race to Dubai still needs to secure some good finishes to retain his card for next season, birdied the fifth and seventh on the way out.
And with back-to-back birdies at the 12th and 13th he went to four under with five to play.
Challenge Tour graduate Colsaerts, the longest hitter on The European Tour this year, also picked up four shots without a bogey through his first 13 holes to share top spot as he searches for a first European Tour title.
Four players were tied a shot further back - England's Ross Fisher and Nick Dougherty joined by Spaniard Gonzalo Fernandez-Castaño and American Cameron Tringale.
|T4||LARA, José Manuel||ESP||18||-9|