Venus Williams remained on course for a strong end to an inconsistent season when the American beat Italy's Francesca Schiavone 6-3, 6-3 to reach the Zurich Open semi-finals on Friday.
Third-seeded Williams will face Serbian second seed Ana Ivanovic on Saturday after the world number four saw off Czech qualifier Petra Kvitova 6-1, 6-4.
Williams has won just one title this season -- albeit at Wimbledon -- and is still looking to gain enough points this week to join younger sister Serena at the season-ending WTA Championships.
Following the second round exits of her nearest rivals for a place, Vera Zvonareva and Agnieszka Radwanska, the former world number one took another big step towards the Doha finale by maintaining her perfect record against the world number 23.
The opening set was a messy affair with Williams eventually coming out on top of a five-game run in which both women failed to hold serve.
The American finally found her rhythm when it counted, serving out to love to end the sequence and seal the set.
In the second set Williams was much more convincing, varying her play nicely to break her opponent twice and take a 4-1 lead.
Schiavone, who had lost all four previous encounters with Williams, briefly threatened to fight back after grabbing a break to make the score 4-2 but slipped up again while serving to stay in the match at 5-3 down.
"There were definitely some back and forth games today but I think overall I played more consistently than in the last rounds," Williams said.
"My main goal was just to keep my own errors down and that always makes it harder for my opponents.
"I'm not counting the points (for Doha). I will just do my best this week and that's it."
Ivanovic owed a good deal of her success on Friday to some terrible serving on the part of her teenage opponent.
Kvitova, ranked 57th in the world, double faulted five times in her second service game to hand the Serb a 3-1 lead.
That formed part of an eight-game winning streak that saw Ivanovic romp through the first set and go 3-0 up in the second.
The French Open winner then suffered some wobbles of her own, inexplicably dropping her next three service games.
Kvitova was unable to capitalise however, twice more failing to hold her own serve in a scrappy end to the match.
Saturday's other semi-final will involve two unseeded players with Italy's Flavia Pennetta taking on Spain's Anabel Medina Garrigues.
Pennetta, who beat world number one Jelena Jankovic in the second round, saw off Slovenia's Katarina Srebotnik 7-5, 6-2 in the quarter-finals.
Garrigues benefited from a shoulder injury sustained by her Belarussian opponent Victoria Azarenka who won the first set 6-4 but retired after losing the second 6-3.