Bernhard Langer, meanwhile, got off to a solid start in his attempt to capture the Charles Schwab Cup, which goes to the winner of the Champions Tour's season-long points race. A $1 million prize also goes to the points winner.
Blake suffered a lone bogey on the Desert Mountain Club's Cochise Course to take a one-shot lead over Gary Hallberg.
Langer comes into the final event of the year on the Champions Tour with a 211-point lead over Tom Lehman in the race for the circuit's most important trophy.
Lehman shot a 68 Thursday, putting him in a tie for 11th place, while Langer was another shot back tied for 18th. If they finished in those positions on Sunday, Langer would easily win the Charles Schwab Cup.
Langer birdied three of his last four holes to overcome a slow start.