Jacobson, who finished Thursday's play by going 4-under over his final three holes, opened and closed his Friday round with birdies and also had a string of three consecutive birdies in getting to 11-under 133 for 36 holes.
Louis Oosthuizen had nine birdies en route to a 9-under 63, which tied the course record at the Sheshan International Golf Club. He is tied for second with Adam Scott, whose second-round 7-under 65 included nine birdies and two bogeys.
Jacobson opened his second round with a birdie at the 10th hole and had three consecutive birdies over Nos. 14-16. He then had eight pars before moving into the lead with birdies at 7 and 9.