With her final error in a mistake-filled performance, Serena Williams said goodbye to a winning streak of 25 matches and hopes of a calendar-year Grand Slam, an achievement many thought entirely possible just a few hours ago. That's how dominant Williams has been against the field at the biggest tournaments, and how unlikely this result—a 4-6, 6-3, 6-3 win by former No. 1 Ana Ivanovic—was today in Melbourne.

But that hardly does Ivanovic’s impressive performance justice. The Serb entered this match having lost all eight sets she played against Williams, and the disparity of their serves was colossal—where Serena is known for hitting aces, Ivanovic is known for catching errant ball tosses. Yet it was Ivanovic who was the superior server, winning 78 percent of her first-serve points and 60 percent of her second serves, both in great contrast to Williams’ numbers. Serena struck 13 aces, but that wasn’t enough balm to repair the damage inflicted by Ivanovic’s damaging returns. She pummeled Serena’s serves—not just second serves—and was the aggressor throughout. It was surprising to see Serena hit 31 unforced errors, but it was even more of a sight to see such bold returning against the greatest server in the history of women’s tennis.

A large portion of these statistics were accrued in the longest set of the match—the first, won by Serena. And that is where Ivanovic’s mental game must be commended. Despite breaking Williams at 2-2 and making inroads on a number of other service games, Ivanovic nonetheless found herself down a set, still unable to break a career-long hex.

Ivanovic remained resolute and did not waver from her strategy whatsoever; perhaps fittingly, she broke Williams at the very same 2-2 juncture in the second set. This time, Ivanovic made the lead hold up. Unable to break back as she did in the opening set, Williams faced a barrage of powerful Ivanovic forehands and returns—along with a few slice backhands that didn’t work as well—and capitulated without much resistance. When Ivanovic closed out the second set with a forehand winner, it was her 18th of the match. Serena had hit just two.

The final act of Ivanovic’s success story saw these themes through to the conclusion. As Serena made uncharacteristic errors, Ivanovic raced to a 3-0 lead. In her next service game, Ivanovic won the first point thanks to a fortunate let cord, but the No. 14 seed didn’t need any bit of luck on this day. It was as skillful a showing from Ivanovic as we’ve seen in years, recalling the days where her strokes were held in the estimable air as Serena’s. And her serve continued to shine: In the pressure-packed 4-2 game, she held at love.

Ivanovic’s return, the shot of the match, remained a constant, continuously putting Serena into 15-30 and 0-30 deficits. Her only mistake came on her first match point, with Serena serving, as an attempted running forehand was struck too hastily and found the net. When Serena fought her way to a hold, Ivanovic needed to prove herself one final time. She did so, with another love hold. And unless you were a fan of Serena Williams—who will be just fine, despite this showing and some reports of back trouble—you had to love what you saw from Ivanovic today.