Vera Zvonareva used to be the kind of player who would fuss when a match didn’t go her way. Friday afternoon in the California desert, this gifted Russian took a big step forward in the world of women’s tennis.

No longer an emotionally volatile performer who would telegraph her feelings to an opponent, Zvonareva allowed Victoria Azarenka to learn about psychology. Zvonareva’s steadiness enabled the fourth-seeded Russian to oust the eight-seeded Azarenka, 6-3, 6-3, in the first semifinal of the BNP Paribas Open in Indian Wells, Calif.

Zvonareva was hardly spectacular on a hot and cloudless day, but the 2009 Australian Open semifinalist played impressive tennis when she had to.

The point that defined this duel in the desert came unusually early, with Azarenka serving at 2-3, 15-all, in the first set. Zvonareva hit a groundstroke that landed in the area of the baseline. Just as Azarenka was preparing to hit the ball, the lineswoman made an “out” call but then immediately corrected herself. Azarenka challenged the call and lost, as the Hawk-Eye replay system showed the ball clipping the back end of the baseline.

This is when controversy entered the stadium court at the Indian Wells Tennis Garden.

The original “out” call naturally affected Azarenka’s concentration and timing. The Belorussian up-and-comer, who just recently broke into the WTA top 10, pulled away from the ball and missed the shot. It’s a mistake for a player to anticipate a call before it’s actually made, but Azarenka was prepared to hit this particular shot.

In light of such a scenario, the point should have been replayed. Instead of making the proper ruling, however, the chair umpire mystifyingly decided to award the point to Zvonareva, who subsquently broke for a 4-2 lead. Once Zvonareva established a clear advantage on the scoreboard, Azarenka–doing what Zvonareva might have done in past years–completely unraveled.

Unnerved by the chair’s poor decision, Azarenka began to spray her groundstrokes into the doubles alleys. When Zvonareva consolidated her break to get a 5-2 lead in the first set, Azarenka called for a coaching time-out, but one could see that this attempt to regain motivation simply wouldn’t work. Azarenka slumped in her chair and projected the attitude of an already-beaten competitor.

Throughout a second set in which Zvonareva held the lead, Azarenka repeatedly threatened to smash her racket. By openly revealing her emotions, Azarenka told her older and wiser opponent that a steady, no-frills approach would be enough to win. It was hardly shocking, then, to see Zvonareva rely on high-percentage groundstrokes and allow Azarenka to implode.

Zvonareva had one scary game when leading 4-3 in the second set, but the No. 4 seed saved three break points–one of them with a rare ace–to gain a 5-3 advantage. A dispirited Azarenka predictably sagged in her following service game, and when Zvonareva registered her second break of the set, the match was all over in just 80 minutes.

Victoria Azarenka is 17-2 on the WTA tour in 2009, but Vera Zvonareva has the same record as well. Two talented players took the court in California, but only one of them had the mental toughness needed to advance to the Indian Wells final.