Webb's 5-under 67 gave her a two-round total of 136 in the rain-shortened 54-hole tournament at Royal Pines. Two regulars on the Japanese tour -- Australian Tamie Durdin and South Korean Shin Hyun-ju -- were tied with Webb, Durdin after a 67 and Shin with a 68.
Taiwan's Tseng Ya-ni and England's Lisa Hall, both with 69s, were tied for fourth, a stroke back of the leading trio.
One of Webb's biggest putts came on the 16th, when she saved par from 16 feet to stay within a stroke of the lead. Webb missed the green on the par-4 17th, but again saved par.
'I just hit a real bad shot on 16, kind of fat,' Webb said. 'But I made a nice putt, then a good up-and-down on 17.'
Webb said she hasn't been hitting her driver well, 'but on this course, you can get away with it.'
'I was hot and cold today,' she said. 'Tomorrow I'll have to hit another low score. You can't be conservative out there.'
Durdin, who played 26 events in Japan last year, was among the early leaders at Royal Pines last year before fading on the weekend.
She double-bogeyed the par-4 4th hole Saturday after taking a penalty drop when her ball landed in trees and under branches, then her bogey putt lipped out. But she had seven birdies the rest of the way.
Durdin, whose best finish in Japan is a tie for fourth, is aware of her reputation of not being able to remain among the leaders.
'I've had trust and belief issues before and I have then obviously failed at the finish line,' she said.
'But it's a question of believing in what I'm doing, trusting myself. I'm doing that now.'
Webb called Durdin 'the biggest underachiever in Australian golf.'
'She has more talent in her little toe than 90 percent of the field this week,' Webb said.
Shin will begin her fourth year on the Japanese tour this season, where she has two career wins.
She had two bogeys on the back nine -- both on par 3s, including a three-putt on the 16th. But she made a 16-foot birdie putt on the ninth -- her last of the day -- to pull into a tie with Durdin.
'My driving is not that long, so my strong point is my short game,' Shin said through an interpreter. 'I am pleased with the way I am playing.'
Seven players were two shots off the lead: former Duke University player and 2002 NCAA champion Virada Nirapathpongporn of Thailand, who shot a 69, Louise Stahle (67) and Anna Tybring (68) of Sweden, Tania Elosegui of Spain (70), and Carri Woods and Diana D'Alessio of the United States and Marianne Skarpnord of Norway, all after 69s.
Former three-time Masters champion Laura Davies of England shot 69 and was at 139, three shots back.
'I drove the ball much better today, I was always in play,' Davies said. 'I missed a few short birdie putts, which was disappointing, but I'm one of the people still around with a chance to win.'
Ai Miyazato of Japan and Shin Ji-yai of South Korea, who lost to Webb in a playoff in last week's Australian Open at Kingston Heath in Melbourne, each had 69s and were tied in the group with Davies.
Australian Nikki Garrett, who held a one-stroke first-round lead over 10 players, had a 73 Saturday and was four strokes back.