The pair had a one-stroke lead over a group of five that included Swedens Oskar Henningsson (66), Wales Bradley Dredge (67), Irelands Peter Lawrie (68), Englands Kenneth Ferrie (67), and Australias Wade Ormsby (67).
Another 10 players were two shots behind, including first-round co-leader Paul McGinley of Ireland.
Clarke, hoping to become the first player to retain the title since American Bob Byman in 1978, birdied the 10th and 12th holes both days, plus the par-3 15th.
Its one of my favorite venues, Clarke said. It sets up well for me and its always nice to come back to a place where youve done well.
Hedblom, looking for his first top-20 finish this season, was at 10 under through 13 holes but bogeyed the last two to drop.
The course record at Kennemer Golf and Country Club was lowered to 63 by Englands Marcus Higley, who was in the group two back, and Spains Alejandro Canizares, who improved from 2 over to 5 under.
McGinley shot 70 and first-round co-leader Gary Orr carded 73 to fall five behind.