With the fourth round of the US Open in the books, it's time to highlight which players are on the rise and which ones look most vulnerable heading into the next round. Players who have been eliminated are of little interest to fantasy owners as the tournament unfolds, so this column is meant to take a look ahead based on what's happened so far rather than reflect on the past.
Every men's singles and women's singles quarterfinals match is touched upon below. Last year's champion on one side should be pleased with their matchup in the next round, while the other defending champ could run into serious trouble.
Novak Djokovic - Djokovic stretched his winning streak in Grand Slam matches to 11 with a convincing, straight-sets triumph over Joao Sousa, once again showing no signs of the vulnerability that peeked through in the first round. He was slated to play Roger Federer here, but Federer was shockingly upset by 55th-ranked John Millman in the Round of 16. Djokovic's 8-2 record in his last 10 Grand Slam matches against Federer suggests he would have been favored anyway, but his odds of advancing are astronomical against Millman.
Rafael Nadal - Nadal survived a third-round scare against Karen Khachanov and dropped a set to unseeded Nikoloz Basilashvili in the Round of 16, but he'll be happy to see Dominic Thiem's name in the quarterfinals. Thiem is an extremely accomplished clay-courter -- in fact, Nadal's lone loss on that surface in each of the past two seasons has come courtesy of Thiem. Hard courts are a different story, however. All 10 of their previous meetings have come on clay, but Nadal should be viewed as a solid favorite in their first hard-court showdown. While both guys have 13 wins on the faster surface this season, Nadal only has one loss while Thiem has accrued four, including a trio of defeats to players ranked outside the top 50.
John Isner - Isner has battled his way into the quarterfinals, winning a pair of five-setters in his first four matches. Meanwhile, Juan Martin del Potro has had a significantly easier time and is yet to drop a set. While Isner's tremendous serve gives him a chance against anybody, he'll have a hard time breaking del Potro's serve and will be the underdog in most of their rallies.
Kei Nishikori - Nishikori lost the 2014 US Open final to Marin Cilic, but he has a great chance to get some revenge here. Despite that 2014 loss, Nishikori leads their head-to-head 8-6 (6-5 on hard courts). The former world No. 4 has seen his ranking slip in recent years due to injuries, but Nishikori appears to finally be back to his old self and has lost only one set through four matches in Flushing Meadows.
Madison Keys - Keys has benefited from a favorable draw, as the highest-ranked player she's faced so far was 29th-seeded Dominika Cibulkova, whom she easily defeated 6-1, 6-3 in the Round of 16. Up next for the American is the No. 30 seed, Carla Suarez Navarro, who celebrated her 30th birthday Monday with a win over Maria Sharapova. Keys leads their head-to-head 3-0, and the hardest-hitting woman on tour should control most of the rallies while drawing energy from the New York crowd against an opponent that's looking for her first career Grand Slam semifinal.
Naomi Osaka - Osaka was finally tested in the Round of 16, but she managed to get through fellow 20-year-old Aryna Sabalenka, 6-3, 2-6, 6-4. In the quarterfinals, Osaka draws 36th-ranked Lesia Tsurenko. It's the first Grand Slam quarterfinal appearance for both women, though this is a natural step forward for Osaka considering she's now reached at least the third round in nine of her first 11 Grand slams played. Meanwhile, Tsurenko's 20-28 record in majors prior to this run suggests this may be the furthest she'll ever get.
Sloane Stephens - Stephens is unmistakably the favorite in this match after consecutive convincing victories over tough opponents, but don't expect this meeting with 19th-seeded Anastasija Sevastova to be a cakewalk. These two met in the quarterfinals of last year's US Open, and Sevastova gave the 2017 champion her toughest test of the tournament. Stephens ultimately escaped in a third-set tiebreak, coming back from a break down in the deciding set. They've split two subsequent meetings, so Sevastova definitely believes she has what it takes to knock off Stephens on the big stage.
Karolina Pliskova - It's weird picking a higher-ranked player as a sleeper, but Pliskova knocking off Serena Williams would certainly go down as an upset considering Williams is the oddsmakers' favorite to take home the title. Pliskova has thrown a wrench into Serena's US Open title hopes before, beating her 6-2, 7-6 (5) in the 2016 semifinals. That victory tied their career head-to-head at one match apiece and they haven't met since. Pliskova hasn't lost a set yet in this tournament, so don't count her out.