Tennis players are known to be creatures of habit. Eating the same prematch meal, bouncing the ball a certain number of times before serving, or using the same one after winning a point, are some of the tour's most common routines. Former World No.1 Justine Henin, for example, was famous for never stepping on the lines when she arrived on court and in-between points.

Defending Australian Open champion Aryna Sabalenka is taking definition to a new extreme this year in Melbourne -- and she's making it a team effort. Before each match of her title defense so far, the No. 2 seed has scrawled her signature on her fitness trainer Jason Stacy's bald head. 

“We just like to do weird s---, guys!” Sabalenka said Sunday to roars of laughter in Margaret Court Arena after a 6-3, 6-2 fourth-round win over American Amanda Anisimova, revealing that she first did it on a whim before her opening-round 6-0, 6-1 win against German qualifier Ella Seidel.

"After I won, I told Jason, ‘Well, I guess it’s a routine right now.'"

Sabalenka, who is featured on Season 2 of Netflix's "Break Point," later said that while Stacy hasn't been "super happy" with the development, to his credit, he's been a good sport about it.

"He's like, 'OK, anything for the win.' I'm like, 'Thank you.'"

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The other takeaway? If it isn't broke, don't fix it.

Sabalenka is currently in the midst of an 11-match winning streak at Melbourne Park, as she has only surrendered 11 games through four rounds of her title defense so far. It is the fewest games dropped through to this stage of the tournament in a decade. (In 2013, Maria Sharapova dropped five, and Serena Williams dropped eight.)

She's also the first player to get this far in her title defense in Melbourne since Williams in 2016, and will face another Grand Slam winner -- No.9 seed Barbora Krejcikova -- in the hopes of reaching her sixth straight Grand Slam semifinal. 

Keep the Sharpies ready.