Webb stands at 13-under-par 203 after 54 holes. She has won three times already this season, including the season's first major, the Kraft Nabisco Championship.
Morgan Pressel knocked her second shot in the water at the last en route to a double-bogey. That capped a round of 3-under 69. Pressel stands at 8-under-par 208 and shares second place with Maria Hjorth, who shot 70 Saturday.
Women's world No. 1 Annika Sorenstam posted a 3-under 69 in the third round. The Swede, who carded five birdies and a double-bogey, was joined in fourth place at minus-7 by Lorie Kane, who bogeyed two of the last three holes, and Mi Hyun Kim.
Webb, who shared the lead entering the third round with Jeong Jang, parred the first four holes. She collected birdies on the fifth and eighth to make the turn at minus-9.
The Australian missed birdie putts from inside seven feet at both the 10th and 11th at Blackhawk Country Club. However, she converted a 18-foot birdie putt at 12 to move two clear of Pressel and Kane.
Webb parred the next three, but was just one clear of Kane. Kane and Pressel were on group in front of Webb. At the par-3 16th, Pressel poured in a 18-footer for birdie, while Kane came up short of the green off the tee and could not save par.
The 31-year-old Webb responded with a birdie of her own on 16 to again move two ahead of Pressel. Webb then kicked in a 5-footer for birdie on 17 and made it three in a row with a 6-foot birdie putt on the 18th.
'I just played really solidly. I only missed one green and I was putting, actually, I missed two greens, but I putted both of them from off the green,' Webb stated. 'I had really good ball striking round. I missed a couple shorter putts, probably three putts inside of seven feet for birdie. I was just really glad that I kept my patience and made one on the next hole.'
Pressel got to 7 under thanks to birdies on three and six. She stumbled to a bogey on the par-3 seventh. Pressel rebounded with birdies on nine and 10 to move to 8 under.
The 18-year-old birdied 13, but gave that stroke right back with a bogey on 14. After Pressel drained her birdie on 16, she came right back with an 7-foot birdie putt on 17.
Pressel landed in a fairway bunker off the tee at the 18th. She hit her second shot fat and it splashed into the water short of the green. Pressel found the green with her fourth and two-putted for double-bogey to end at minus-8.
'Obviously, you're disappointed anytime you double the last hole after putting yourself in such a great position you're upset and I'm upset,' Pressel stated. 'I made a great putt on 16 and a good birdie on 17. You know I played pretty solid today except for one shot, maybe two shots I guess, but that happens.'
Hjorth collected three birdies and a bogey over her opening nine holes. Around the turn, she birdie 11, but bogeyed the next two holes to drop to 7 under. She recovered those lost strokes with birdies at 15 and 16. Hjorth closed with a bogey on the last to share second with Pressel.
Nicole Castrale carded a 5-under 67 to move into a share of seventh place. She stands alongside Jimin Kang, Cristie Kerr and Stacy Prammanasudh at 6-under-par 210. Il Mi Chung, Jeong Jang and Kelli Kuehne are one stroke further back at minus-5.