Sweden's Annika Sorenstam and Silvia Cavalleri of Italy share fourth at 7-under 209.
With 18 holes remaining, Webb has put herself in position to become the first professional golfer to win five consecutive tournament titles. The Australian shares the current record of four straight titles with the likes of Gene Sarazam, Walter Hagen and most recently Laura Davies, who captured the Standard Register PING from 1997 to 2000.
'I'm thinking about it a little bit, but I have to think about winning the tournament first,' said Webb. 'If I don't win it, I don't win five in a row, I have to do that first.'
The 27-year-old started her round with back-to-back birdies from the third and added two more at Nos. 10 and 12. She moved into a tie for the lead at 11-under with a birdie at the 15th while Esterl bogeyed the par-three 14th.
Webb parred the next two holes before bogeying the final hole. However, Esterl made bogey at the 17th to keep the pair knotted atop the leaderboard.
'There is a lot of work to be done and there are a lot of good players on the leaderboard, so I'll have to put in a good one tomorrow,' said Webb.
Charlotta Sorenstam carded a 70 to stand alone in sixth at 6-under 210. She is followed by a pair of Australians in Wendy Doolan (71) and Cherie Byrnes (71).