MELBOURNE—Three years ago I wrote an article about Maria Sharapova entitled “The Art of Ignoring.” It was, as you can probably guess, about her signature trait as a tennis player, her ability to shut everything out. Double faults, unforced errors, criticism of her so-called “mindless ball bashing,” and even more criticism of her trademark shrieking: Sharapova plays through it all, seemingly without a second thought or a care for what anyone thinks of her. On Thursday in Australia, though, she had something new to ignore, and it could have been the most dangerous distraction of all: The heat. By the time Sharapova started her third set against Karin Knapp, it was 111 degrees in the air, and perhaps much more on court in Rod Laver Arena.

Adding insult to injury, Australian Open officials waited until the two players had reached 5-4 in the third set, with Sharapova serving for the match, before invoking the event’s Extreme Heat Policy. This meant that when each match on the grounds reached the end of the current set, play would be suspended; in Laver and Hisense Arenas, play would resume once the roofs were closed. About time—except, unfortunately, for Sharapova and Knapp. Their deciding third set couldn’t end in a tiebreaker. When Knapp broke for 5-5, the possibility of a lot more tennis in the extreme heat soon became a reality. (Afterward, Sharapova said, sensibly enough, that the heat rule should leave room for discretion in sets that don't end in tiebreakers to stop them at 6-6.)

Up until then, it hadn’t been Sharapova’s finest couple of hours on a tennis court. She would finish the match with 12 double faults and 67 errors against 34 winners. She squandered 13 of 20 break points—many on errant returns of second serves—and was broken nine times. At 5-4, with the roof ready to close, she reached match point three times, but was denied on all three. Sharapova spent as many precious seconds as she could hiding in the shade at the back of the court, and had to be veritably de-iced after each changeover. She tried to finish points quickly, but most of the time she ended up going for too much, both on her ground strokes and her second serves. This is one more thing that Sharapova tends to ignore: Percentages.

As the third set progressed and her opponent refused to go away, Sharapova grew visibly unhappy and slump-shouldered, and she understandably annoyed when she assessed a time warning for taking too long between points—Knapp, on average, was taking longer. Sharapova's one moment to savor was a rare correct line-call challenge on a backhand winner. She celebrated, appropriately, with a fist pump—after walking back into the shade, of course.

But credit Knapp for bringing Sharapova so close to the edge. The 26-year-old has suffered through a heart ailment and two knee surgeries, yet she’s a respectably ranked No. 44. She pushed back against Sharapova with her forehand, but couldn’t connect on the big shot when she needed it. Knapp has never beaten a Top 10 player, and it showed in the wild, nervous errors that inevitably flew off her racquet whenever she came near the finish line.

With Sharapova forced to serve to stay in the match every two games, and with her motion as shaky as ever—she double faulted eight times in the third set alone—it was easy to foresee a quick Knapp service break ending it. Knapp reached 30-30 twice, but while Sharapova would bend, she wouldn’t be broken. She kept going after her shots, even when they weren’t clicking, and found quality serves when she had to have them. At 5-6, she held with a hard slice second serve down the T. That shot alone was probably worth three double faults on less-important points. The best players, you might say, play by their own percentages.

Sharapova threw in three more double faults when she served for the match a second time, at 9-8. But on break point, she somehow found the outside half of the sideline with a desperately slapped backhand. At deuce, she came up with another service winner. And at match point, her fourth, she watched as a Knapp backhand sailed long. Sharapova had won 6-3, 4-6, 10-8 in three hours and 28 minutes. The last set was the longest, in total games, she had ever played. Depending on what happens the rest of this tournament, the match may go down as a signature victory in the career of one of the game's most famous fighters.

“I didn’t play my best tennis,” Sharapova said afterward. “I didn’t do many things well.”

In her world, those are just two more things a winning tennis player has to ignore.