Grace Park, Jeong Jang, Pat Hurst and Juli Inkster share second place at four- under-par 68.
Annika Sorenstam, the top player in the game, withdrew after six holes on Thursday. She cited the cold she caught last week at the U.S. Women's Open and left the course on her seventh hole after she was one-over par for her round.
'I feel bad for the fans and the tournament, but my whole body feels ill,' Sorenstam said in a statement before leaving Point Grey Golf and Country Club. 'I tried my best to play today and I apologize to the fans, but I need to go home and get better.'
Bowie began her round on the back nine at Point Grey and promptly broke into red figures. She played a three-wood just short of the green at the par-five 10th and chipped to three feet where she converted the birdie putt.
At 13, Bowie knocked a six-iron to seven feet to set up birdie but she dropped a shot two holes later when she missed the green right and could not get up and down.
She recovered at the par-four 16th when she drained a 20-foot birdie putt and closed her front nine with a four-foot birdie at the par-five 18th.
Bowie once again took advantage of the par-fives at Point Grey when she reached the green in two with a five-wood at the third. She holed a 40-foot eagle putt to get to five-under on her round and take sole possession of first place.
She added to her lead at six when she hit a nine-iron to 15 feet and ran home the birdie putt.
'I didn't get into too much trouble and kind of took advantage of my opportunities,' said Bowie. 'I don't think it's out of the blue. I played well last week and I think I've been right on the cusp of it and maybe it's coming together now.'
Bowie also benefited from playing with Kelly Robbins on Thursday. Robbins, who lost in a playoff at the U.S. Open Monday, was five-under par until a double-bogey at her last cost dropped her to three-under.
'I was just playing how Kelly was playing,' said Bowie. 'She was right there the whole time. You definitely do feed off each other. I didn't ever start thinking about the fact I was six-under.'
Inkster mixed two birdies and two bogeys on the front nine but caught fire on the back nine. She sank a three-footer at the 10th, a pair of six-footers at 14 and 17 and narrowly missed eagle at 18 when her putt stopped inches short of the hole.
'I'm very happy with the way I played on the back side in my round,' said Inkster, a Hall of Famer who won last year's U.S. Women's Open. 'I'm looking forward to trying to continue what I'm doing.'
Park had a simple round on Thursday. She drained a 12-foot birdie putt at 17, her ninth, and then holed a 10-foot eagle at three and a 15-foot birdie putt at four to gain a share of second.
Hurst and Jang, who made it near the top of the leaderboard on Sunday at the Open until a quintuple-bogey on her front nine, each tallied six birdies and two bogeys on their rounds for their 68s.
Robbins, defending champion Meg Mallon, Laura Davies, Young Kim, Se Ri Pak, Julie Piers, Leta Lindley, Beth Daniel and Soo-Yun Kang share sixth place at three-under-par 69.