If Maria Sharapova is to add to her five Grand Slam titles she will again have to navigate a matchup that arguably, for better and, for so long, for worse, has defined her career. For the 21st time, and for the third time in the last five Grand Slams, Sharapova will go head-to-head with Serena Williams.

In terms of name recognition it is the biggest rivalry in women’s tennis, but in terms of what has transpired on the court between the two in recent years, it has barely been a rivalry at all. It all started so brightly for Sharapova. At the age of 17, she announced herself as women’s tennis next superstar by not just beating but eviscerating the previously dominant Williams in the final of the 2004 Wimbledon. But since their next meeting at the end of that year, Sharapova has not won once. Indeed, in 17 matches, Sharapova has won just three sets.

Included in that run have been six Grand Slam meetings, with perhaps the most notable being the final of the 2007 Australian Open, when an unseeded Williams sensationally shook off the rust to sweep Sharapova aside for the loss of three games. They met in the final in Melbourne a year ago, too, when again Williams won in straight sets.

Still, at least the Russian made a fight of it that time around, and can perhaps take confidence from the way she forced a tiebreak in that second set as she prepares for their quarterfinal at Melbourne Park on Tuesday.

After so many losses, Sharapova insists that she will approach the match in a positive mindset, while trying once again to find ways to improve.

“It's not like I think about what I can do worse,” she said, after beating Belinda Bencic in the fourth round “You're always trying to -- always trying to improve. I got myself into the quarterfinal of a Grand Slam. There is no reason I shouldn't be looking to improve and to getting my game in a better position than any other previous round. It's only going to be tougher, especially against Serena.”

Sharapova can take belief, too, from the way she played in beating the talented Swiss Bencic 7-5 7-5. In particular, the fifth seed served superbly, firing down 21 aces. With her serve for so long being one of the major weaknesses against Williams, it will be a statistic she will be desperate to replicate when they meet on Rod Laver Arena.

But Williams has been in fearsome form herself. After a tough opening match against Camila Georgi, the American has won her next three rounds for the loss of just eight games. The doubts that existed about Williams’ fitness coming into the tournament, having not completed a match since her painful semifinal loss at last year’s U.S. Open, have already been answered emphatically.

And, while the defeat to Roberta Vinci that ended her hopes of a Calendar Grand Slam took some time to get over, both physically and emotionally, there is plenty now to play for. Notably, the 34-year-old is just three wins away from equaling Steffi Graf’s Open-era record of 22 Grand Slam titles.

A match with Sharapova has also appeared to act as a powerful motivation for Williams in her career. Still, she insists that she is taking nothing for granted as she prepares to face her rival once again.

“Every match is new,” she said after beating Margarita Gasparyan 6-2 6-1. “You know, she always brings in something new and something special. She's very consistent, as well. Yeah, she knows how to be -- one player that's always consistently winning and training and working hard and winning matches.”

Prediction: Last year’s meeting at the Australian Open was one of the more competitive between the pair. And, if Sharapova can replicate her serving performance against Bencic, then she could make a real match of Tuesday’s quarterfinal. However, attempting to serve 21 aces against the fearsome return of Williams is a very different prospect, and so often Sharapova has fallen apart under the pressure the world No. 1 exerts from the other end of the court. The simple fact is that Williams does everything Sharapova does, but better. And, while Williams can often take her eye off the ball to allow chances for some players, she always faces Sharapova with the most focused determination. Unless Williams’ game falls apart, it will be another win, very likely in straight sets.

Match start time: Not before 8:45 p.m. EST, following the match between Agnieszka Radwanska and Carla Suarez Navarro, which will get underway at 7 p.m.

TV channel: Tennis Channel has coverage from 7 p.m. to 9 p.m., with ESPN2 then taking over.

Live stream: ESPN3, Watch ESPN