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Victoria Azarenka’s blond braid bounced against her back as if keeping the beat of her fast feet, tap-dancing behind the baseline. Playing as if propelled by music she heard in her head, Azarenka got in a smooth groove early and left Li Na looking as displaced as a woman seeking a seat when the song stops during a game of musical chairs.

The fourth-ranked Belarusian barely made a misstep in a brilliant, 6-2, 6-2 beatdown to extend her winning streak to seven matches and storm into Saturday’s semifinals of the WTA Championships in Istanbul. Azarenka has swept U.S. Open champion Samantha Stosur and reigning Roland Garros winner Li in succession, and has won 16 straight sets since falling to Agnieszka Radwanska in the Tokyo semifinals in September.

Intent on taking the first strike in rallies, Azarenka served at an eye-popping 89 percent in the first set, giving Li only three looks at her second serve during the opener. She did not face a break point in the match, while Li confronted 11 such obstacles.

"Li Na is such a good returner so I had to try to take that away from her," Azarenka—who built 5-1 leads in both first and second sets—told Tennis Channel’s Katrina Adams.

Azarenka’s fast service games had a cumulative, oppressive effect on her opponent, who held a 1-0 lead when she drew an easy forehand sitter near the net but fired a forehand three feet long in a mind-numbing error that would make most hackers cringe in horror. If Li had made the shot it would have given her double break point; the miss signaled a crack in confidence, as Azarenka ran off five consecutive games to seize command, sealing the opening set in 43 minutes.

Even when Li did manage to hold it was a taxing task. Two of her first three service holds spanned more than seven minutes, as she began to wear the wide-eyed expression of someone who couldn't find a safe spot on the court to prevent Azarenka from ripping a reply. This wasn’t bash and smash tennis. Azarenka, who is not as quick around the court as Li, anticipated well, defended brilliantly and played both sharp angles and deep drives with equal effectiveness.

Li’s husband and coach, Jiang Shan, urged her to engage Azarenka in more forehand-to-forehand rallies—a pattern Li had exploited in winning four of their prior five matches, including straight-sets wins at the Australian Open and Roland Garros. But Azarenka had an answer for everything as Li, who made 19 errors in beating Maria Sharapova yesterday, finished with 32 errors today.

Li made tennis history as the first Chinese singles player to master a major, but Li's streaks are as glaring as Azarenka's shrieks. The erratic Li won 11 consecutive matches to open the season in reaching the Australian Open final before suffering a five-match losing streak. Since her inspired run to the Roland Garros title in June, Li has managed to win back-t0-back matches just once, but still has a shot to reach the semifinals if she beats Stosur tomorrow.

—Richard Pagliaro