Nick O'Hern, who held the first-round lead, picked up eight points for the second straight day and stands at 34 points alone in second place. Scott Gardiner posted 11 points to move into third place with 32 points, one clear of Australian amateur Nick Flanagan, the reigning U.S. Amateur champion.
Play is contested using the Modified Stableford Scoring system. The system offers eight points for a double-eagle, five points for an eagle and two points for a birdie. No points are handed out for par, and one point is deducted for each bogey with players losing three points for double-bogey or worse.
With the attention Laura Davies had during the first two rounds now gone, the field focused its energy on catching Webster. However, the Englishman would have none of it.
He dropped in back-to-back birdies from the third at Horizons Golf Resort to move to 31 points. That broke an early tie for the lead created by Stuart Bouvier, who racked up a day-three high 18 points in the first group to play the third round.
Webster had more magic up his sleeve too. He drained a birdie try at the par-4 seventh and came right back with a birdie at the next.
The 29-year-old picked up another birdie at the par-5 12th. He again came right back with a birdie at the following hole to raise his point total to 39, but trouble loomed.
With a healthy lead, Webster stumbled to back-to-back bogeys from the 14th to slide back to 37 points. He erased those mistakes with a birdie at the par-5 16th, his third in three days on that hole. With that final birdie, he moved back to 39 points and five points clear of the field.
'I've never led a tournament before, so it's a new experience,' said Webster. who is looking for his first professional win. 'I was really in a mess last Saturday, my posture, my alignment and my ball position was all out. So it really felt strange how Ian Woosnam told me to set up but I did a good three hours and the rewards are sweet, really.'
Webster has a solid game plan despite having never won as a pro.
'I've just got to go out there and focus on each shot,' Webster said. 'You've just got to play one shot at a time with this format. It's a course set up for birdies, so I've got to keep my foot on the gas with the birdies. I'm just going to play tomorrow and see what happens.'
O'Hern began his day one point behind Webster but lost ground when he bogeyed the par-4 second. He erased that error and caught Webster as he ran off three straight birdies from the third to tie Webster with 31 points.
As Webster continued his hot play, O'Hern held his ground with five pars in a row, before picking up his fourth birdie of the day at the 12th. Like Webster, he also bogeyed the 14th to drop to 32 points. O'Hern closed with a birdie at the last to get back within five of the leader.
Ricky Barnes, the 2002 U.S. Amateur champion, racked up 16 points to move into a share of fifth place with 30 points. He is joined there by Thomas Levet, who notched seven points Saturday.
Paul Casey, the defending champion, shares seventh place with Joakim Haeggman, David McKenzie, Toru Suzuki, Lian-Wei Zhang and Peter Fowler at 29 points. Gary Evans and Fredrik Andersson are one point further back with 28.