Clarke won the Senior British Open last month at Gleneagles.
"It's nice to win any time, but obviously winning a senior major was more special and I feel good about my game right now," Clarke said. "That's not to say I'll have another couple days like I did today, but I'm going to do my best."
Singh opened birdie-birdie-eagle.
"Played nicely, kept the ball in play, which you need on this golf course," Singh said. "Just tried to make a lot of birdies."
Miguel Angel Jimenez, the Boeing Classic winner last week outside Seattle to match Alker and Jerry Kelly for the tour victory lead with three, shot 72. John Daly, the winner of the PGA Tour's 1992 B.C. Open at the course, also had a 72.
Defending champion Cameron Beckman shot a 73.