(CNN) -- Serena Williams maintained her dominance of Denmark's former world number one Caroline Wozniacki with a typical fightback in the quarterfinals of the Rogers Cup in Montreal.
Williams has only lost once to Wozniacki in eight meetings, back in 2012, but looked in danger of a rare defeat when she trailed a set and 4-2.
The world number one fell 15-30 on her next service game before hammering home one of her 15 aces of the day on the way to a run of 10 straight points to level at 4-4.
A further break of service saw Williams take the second set and she led 2-0 and 4-2 in the decider.
Wozniacki, who was playing some of her best tennis of the year, twice leveled but the top seed pulled ahead again to close out the match 4-6 7-5 7-5 in two hours 41 minutes.
It was to set up a semifinal match with her elder sister Venus, who later also came from a set down to beat Carla Suarez Navarro.
The Spaniard had put out Maria Sharapova in the last 16 and she led Williams a set and 2-0 before the seven-time grand slam champion hit back.
She won 10 of the next 11 games to go 4-1 up in the decider and although Navarro briefly rallied she was always trailing.
Venus eventually closed it out 4-6 6-2 6-3 in two hours 11 minutes to earn her 25th career match up with Serena, who leads 14-10 in wins.
At the men's Rogers Cup tournament, the Masters 1000 event in Toronto, Jo-Wilfried Tsonga continued his fine run with a three-set victory over former Wimbledon champion Andy Murray.
13th seed Tsonga had won the first set on a tiebreak, but after Murray had leveled at one set all, the Frenchman trailed 0-3 in the decider and looked set to go out.
However, he rallied to win six of the next seven games to reach the semifinals.
Tsonga, who beat top seed Novak Djokovic in the previous round, will take Bulgaria's rising your star Grigor Dimitrov for a place in the final.
Dimitrov, the seventh seed, accounted for South Africa's Kevin Anderson in a marathon three-setter 5-7 7-5 7-6.