Australian star Karen Murphy followed up a brilliant comeback victory with a tough loss to an in-form Caroline Brown of Scotland on day two of the World Cup at Warilla Bowling Club.
Murphy recorded her second tie-breaker win in three matches with a fighting victory over Japan's Hiroko Emura in Wednesday's round three.
Emura won the first set 12-5 before Murphy countered with some of the best bowls of the tournament in the nine-end second set, taking it 26-3 then winning the three-end tie-breaker 4-0.
A 26-shot set was easily the highest of the championships.
"I actually was holding one on the final end before she picked up three, but overall it was a very satisfying set and tiebreak," Murphy said.
She then suffered her first defeat against Scottish star Brown, beaten 8-6, 10-3.
Earlier on Wednesday Brown upset four-time defending champion Jo Edwards of New Zealand and now has a great shot of winning the section and advancing straight into Tuesday's semi-finals.
Murphy plays another key rival in South Africa's Colleen Piketh on Thursday, then takes on Edwards on Friday.
Defending men's champion Warilla's Jeremy Henry made it three straight wins and pushed his claims for top spot in his section.
After needing an extra end tiebreak to beat Singapore's Christian Huange in round one, Henry beat New Zealand's Shannan McIlroy in round two and on Wednesday overpowered China's Esmond Lee 16-4, 14-4.
Northern Ireland superstar Henry has won the World Cup for the past two years while he represented Warilla and Australia and had the first of his two byes on Wednesday afternoon.
Henry takes on Scotland's world indoor champion Stewart Anderson on Thursday in a showdown that could decide the section winner.
Anderson had a bye in his opening two matches before beating Isle of Man's Clive McGreal and then Huange in straight sets on Wednesday.
The second and third-placed players in each of the men's and women's two sections qualify for Monday's sudden-death playoffs.
Tony Wood, who claimed the second Australian men's spot in the draw by virtue of winning the Australian indoor title, bounced back from two early losses to beat Fijian Samuela Tuikiligana in straight sets in round three.
Wood takes on Turkey's Ozkan Akar in round five on Thursday morning.
The nine-day indoor World Cup features bowlers from more than 20 nations with Warilla hosting the event for a ninth time.