Former world number one Victoria Azarenka thrashed Australian Ashleigh Barty 6-4, 6-2 to reach the Pan Pacific Open quarterfinals on Thursday as she seeks a return to the top after giving birth in late 2016.
The Belarusian, who slipped further down the rankings as a result of a lengthy custody battle over baby Leo, will face either top seed Caroline Wozniacki, who is chasing a hat-trick of Tokyo titles, or Italy's Camila Giorgi in the last eight.
Wildcard Azarenka, currently 63rd on the women's WTA rankings, broke for 4-3 with a dipping backhand and clinched the opening set with a fizzing pass that landed on Barty's shoelaces, forcing the seventh seed to dump a forehand into the net.
Azarenka raced to a 4-1 lead in the second set and the two-time Australian Open champion delivered the coup de grace by jamming up Barty with a vicious kick serve into the ribcage on her second match point.
Earlier, Czech Barbora Strycova won a tempestuous encounter with Estonia's Anett Kontaveit 7-6, 3-6, 7-5 to set up a quarterfinal against Japan's newly crowned US Open champion Naomi Osaka.
The Olympic doubles bronze medallist took the first-set tiebreak 7-5 but both players screamed in frustration at their wastefulness in a contest that lasted well over three hours.
Having used all her challenges, Strycova huffily staged a sit-down protest after Kontaveit saved one of eight match points with a passing shot that replays showed missed the line by some margin.
But the Czech returned to her task and closed out the match when Kontaveit whiffed a drive-volley far beyond the baseline.
Wawrinka in last 8
Three-time Grand Slam champion Stan Wawrinka advanced to the quarterfinals of the St Petersburg Open on Wednesday with a win over Russian fourth seed Karen Khachanov in two tie-break sets.
The 33-year-old Swiss star Wawrinka, a wildcard entry, knocked off world number 24 Khachanov 7-6 (12/10), 7-6 (7/1) and awaits the winner between defending champion Damir Dzumhur and Guido Pella.
Fifth-seeded Spaniard Roberto Bautista Agut and Canada's Denis Shapovalov, the seventh seed, reached round two with respective wins over qualifiers Luca Vanni, 7-5, 6-2, and Adrian Menendez-Maceiras, 7-6 (7/3), 6-2.
Martin Klizan of Slovakia upset Italy's second seed Fabio Fognini, the man he beat in the 2012 final, 6-3, 6-4.
In the quarter-finals, the left-hander will face the winner of the clash between Shapovalov and Italian Matteo Berrettini.
Meanwhile, 36-year-old veteran Mikhail Youzhny, who is playing the final event of his career, won 7-6 (8/6), 6-4 his opening round match against Mirza Basic of Bosnia.