MELBOURNE, Australia -- The first time the Williams sisters reached the fourth round of a Grand Slam together was the 1998 French Open, when they were still teenagers. They reached the fourth round many times afterward, of course -- as well as advancing much further -- but the most recent time they both played the second week of a major was at Wimbledon in 2011, the year Venus was diagnosed with the autoimmune disease Sjogren's syndrome.

Venus is now 34, Serena is 33, and many of the players they competed against -- even ones younger than they -- are retired. But not the Williams sisters -- no, not even close. They are still playing and still winning, including advancing to the second week of a Grand Slam again after each won her third-round match Saturday at the Australian Open.

Serena Williams started sluggishly but won 12 of the final 14 games to win her third-round match. AP Photo/Rob Griffith

While everyone continues to debate which young American will eventually take the torch from the Williamses, the sisters still do not appear ready to hand it off any time soon. Serena has been No. 1 for 100 weeks, while Venus has pushed her way back inside the top 20 and looks like she will go even higher.

Who will ever take over their mantle? The way they are going, perhaps someone currently young enough to be as interested in an Elsa "Frozen" dress as a Grand Slam championship. Heck, they beat opponents 13 and 11 years younger, respectively, than they are Saturday.

"I think we talk more about all the players we see that aren't playing anymore," Venus said when asked whether she and Serena discuss upcoming younger players. "We just can't figure out how we're still here."

Granted, for a moment Saturday, it looked as if one or both sisters would not get past the third round. Venus was one game from getting knocked out in her match against 23-year-old Camila Giorgi on Margaret Court Arena, while a sluggish Serena was getting hammered in her first set against 20-year-old Elina Svitolina on Rod Laver Arena.

Serena lost her first set to Svitolina 6-4 and clearly needed a pick-me-up. She got it not by ordering an espresso this time, but by looking up to see her older sister had rallied against Giorgi to win the second set in a tiebreaker, then roared to a 4-1 lead in the third set (and eventually won 6-1).

"I thought, 'Wow, she's been through so much with her illness, with everything that she's had to do. Gosh, if she can do it, I'm perfectly healthy, I'm fine. I should be able to do it, too,'" Serena said. "It just got me so motivated, really helped me push through those next two sets at a rapid rate."

Serena did so and more than duplicated her sister's comeback by beating Svitolina 6-2, 6-0. It certainly wasn't the first time the sisters have motivated each other. And it's looking as if it won't be the last.

"I've been motivated by Serena since day one," Venus said. "She's always been someone that anyone can learn from -- the way she faces her life, the way she is fearless on the court."

Venus Williams is into the fourth round of a Grand Slam for the first time since Wimbledon in 2011. AP Photo/Bernat Armangue

The two could possibly face each other in the semifinals, but first, how much further will they go this tournament? Both sisters face a tough fourth round. Venus plays No. 6 Agnieszka Radwanska, who hasn't dropped a set this tournament and beat Williams in the finals at Montreal last year. Serena plays Garbine Muguruza, who knocked her out in the second round of the 2014 French Open. Asked about her memories of that match, Williams said, "Losing."

"But it was a good loss," she said. "As angry as I was, it was the best loss I had the whole year last year. I had a lot of them, but that one in particular made me realize what I needed to work on. It opened my eyes toward a lot of things. I was like, 'Oh, my gosh, if I don't change, then I'm going to be forever in the same position.'"

Serena says making the fourth round of a major is "like party time." As for Venus, despite her impressive comeback from illness, injury and age -- she was No. 103 at the end of 2011 and No. 49 at the end of 2013 -- she downplayed reaching this far for the first time in four years.

"I've won big. It's not like I haven't done it before," the seven-time Slam champ said. "I said this the other day" I like to win titles, whether it's a smaller event or a big event. That's what I play for. So yes, it's great to be in the second week. But is the fourth round my goal when I come to these tournaments? No."

That attitude might explain why these two women are still playing. And winning.