Here's a deep, philosophical question: Is reaching the fourth round at the Australian Open synonymous with that oft-stated goal of "making the second week" at a major?
It's a legitimate query fourth-rounders only make the second week for certain at Wimbledon, where there is no play on the middle Sunday of the tournament. All the fourth-round matches are played on Manic Monday.
At the other majors, many fourth-round players stumble out on Sunday. So, can you still claim "second-week player" status? The problem is semantic. Saying you made the second week sounds like a heftier achievement than saying you made the fourth round. The obvious solution: eliminate Sunday play at the other three majors.
Here are Sunday's fourth-round matches we find most compelling:
No. 3 Grigor Dimitrov vs. No. 17 Nick Kyrgios (Dimitrov leads series, 2-1)
Sometimes, it all comes together perfectly at just the right time. This is one of those occasions. Two hugely talented players trying -- with some success -- to overcome their shortcomings meet with a Grand Slam quarterfinal berth at stake. Expect explosive shot-making and a clash that may land on the short list for "most entertaining" honors.
Dimitrov's greatest advantage over Kyrgios may simply be four years. Both men have been slow to mature, but at 26, Dimitrov, once saddled with the nickname "Baby Federer," finally seems to have figured out how all the pieces of the Grand Slam contender's puzzle fit. He has had a lot of help in that quest from his coach, Dani Vallverdu, since June 2016. Their relationship has been dynamic, and he has convinced Dimitrov that he can succeed at the highest level. That's the best a coach can do.
Kyrgios is just 22 and has been the subject of even greater hype and scrutiny. Plus, he's mercurial and twitchy, unlike laid-back Dimitrov. Kyrgios has been curiously reluctant to appoint a full-time coach, which may help explain why he has been so slow to crack the competitor's code. That may prove a handicap in this match, where steady nerves and emotional stability may count for a lot.
Kyrgios swept past Dimitrov in three sets in the semifinals on his way to the final just weeks ago in Brisbane. Kyrgios also beat his former idol, Jo-Wilfried Tsonga, in the third round the other day despite Tsonga dominating almost every important statistical category (including winners and service breaks). The reason: Kyrgios' superior play in tiebreakers. It's something Dimitrov will have to think long and hard about, as tiebreakers will likely play a major role in the match.
No. 2 Caroline Wozniacki vs. No. 19 Magdalena Rybarikova (Wozniacki leads 3-1)
The bottom half of the draw is Wozniacki's to lose, and now that she has survived the first three rounds, it's unlikely her game -- or her nerves -- will desert her. This start to 2018 looks like a wonderful reward for the year she just completed. Given that Wozniacki might very well be ranked No. 1 by the end of next week, a quick reminder is in order: In 2017, she reached 10 finals (2-8), led the tour in wins (60) as well as top-10 wins (14-5) and vaulted from No. 19 to No. 3, but there was still no major title.
Rybarikova has her work cut out, but the 29-year-old Slovak is a dangerous player who likes to play aggressively, as her excellent grass-court record shows. Rybarikova left the tour after she lost at Wimbledon in 2016 to undergo wrist and knee surgeries. She returned in February 2017 with a ranking of 200 and improved steadily. She won 18 of 20 matches on grass and made the Wimbledon semis, putting her within striking distance of the top 20. She ended the year in that elite company.
The series record is deceptive, because they haven't played since 2014. Rybarikova's lone win is ancient history, having come in 2009. However, if she hopes to repeat it, she will have to hit through the most accomplished pure defender on the WTA Tour and perhaps hope that the magnitude of this developing opportunity causes Wozniacki to succumb to nerves.
No. 10 seed Pablo Carreno Busta vs. No. 6 seed Marin Cilic (Cilic leads, 1-0)
Has there ever been a less heralded fourth-round match between two players seeded within the top 10? Well, blame it on the ultralow profile of both men. Carreno Busta is a Spanish baseliner, presumably a clay-court expert. Cilic is an introverted former US Open champion who seems to struggle to find the inspiration to contend at the majors on a regular basis.
But there's no doubt Cilic can beat anyone when he is enthusiastic, motivated and confident. He demonstrated it again at Wimbledon, where he belted his way to the final opposite the winner, Roger Federer. Cilic's scores in Melbourne have been convincing. When the 6-foot-6 Croatian's serve is working, he produces aces like an ATM machine spitting out 20s. He backs it up with a heavy forehand and, at his height, the relatively slow hard courts put most opponents' shots right in his wheelhouse.
Carreno Busta has won three titles in his career, two of them on hard courts like those at Melbourne Park. Like most Spanish players, he's very fit, but much will depend on how well he handles the Cilic serve and the forehand he likes to back it up with. Carreno Busta's career record against fellow top-10 players is a disappointing 1-19, with the lone win coming over then-No. 6 Milos Raonic.
Upset special: No. 86 Andreas Seppi over No. 49 Kyle Edmund
Seppi is a crafty, 33-year-old veteran who knows how to flummox superior opponents. He showed that in his upset of Federer on these same courts in 2015. That could spell trouble for 23-year-old rising British star Kyle Edmund.