Only 16 men and women will be left standing at the 2013 Australian Open after Monday's Day 8 singles action.
All four are considered legitimate threats to win the Aussie Open title, but they aren't out of the fourth-round woods yet.
Here we break down a trio of pivotal Round of 16 matches set to unfold on Monday.
In an all-French matchup on Day 8, Jo-Wilfried Tsonga will take on Richard Gasquet. Both contenders have cruised through the first three rounds of play, but if there's a clear-cut favorite, it's got to be Tsonga.
The 2008 Australian Open runner-up has slimmed down and looks to be getting stronger as the tournament wears on. He hasn't needed more than three sets in any of his three match wins, plus he's winning a tremendous percentage of his first-serve points.
Although Gasquet is doing the same, I don't like his chances going up against a player as powerful as Tsonga.
We're talking about a player in Tsonga who came from two sets down to defeat Roger Federer in the quarterfinals at Wimbledon in 2011.
If you still doubt Tsonga's chances, consider that Gasquet has never been beyond the fourth round of the Aussie Open.
Serena Williams (3) vs. Maria Kirilenko (14)
There's only one Day 8 women's singles match that will feature two seeded players, and that's Serena Williams vs. Maria Kirilenko. This fourth-round match has tons of potential, but with Serena seemingly destined for the semis, it's nearly impossible to concoct a scenario that puts the Russian through to the quarters.
Aside from committing more unforced errors in each match since the start of the tournament, one could argue that Williams has actually improved since her dominant first-round win a week ago.
She has been recording more and more winners every round and showing off her sensational serve while racking up devastating aces in the process.
As talented as Kirilenko is, she isn't on Williams' level, and that will show on Monday. She doesn't possess a big serve or any other overwhelming strength that can provide easy points against Williams.
With that in mind, I like Serena to steamroll into the quarters on Day 8.
Andy Murray (3) vs. Gilles Simon (14)
Another Day 8 matchup with tons of promise will pit reigning U.S. Open champion Andy Murray vs. Gilles Simon of France.
Simon survived an epic third-round clash with fellow French player Gael Monfils on Day 6. He will need his A-game and then some in order to oust Murray en route to the quarters.
Despite that fact, Monday's matchup is sure to feature some twists and turns. Simon is battle-tested if nothing else, having played 13 sets in three matches.
Also, Simon is Murray's first seeded opponent in Melbourne this January, which means Murray will have to take his game to the next level in order to cruise into the quarters.
Follow Bleacher Report Featured Columnist Patrick Clarke on Twitter throughout the 2013 Australian Open for more reaction and analysis on the year's first Grand Slam.