Six-time US Open champion Serena Williams continues her quest for her 23rd Grand Slam singles title, and an unprecedented seventh title in Flushing Meadows, and it is the Grand Slam title she hasn't won recently with the last one coming in 2014.
Fifth seed Simona Halep survived an almighty scare in the third round with 31st seed Timea Babos in the third round, however, the Romanian is still in the hunt for her first Grand Slam singles title, and has already had the experience of competing in a Grand Slam final at the French Open in 2014 losing to Maria Sharapova in three tight sets.
The top seed continues to make history and she has the most victories at Grand Slam in the Open Era with 308, one more than 17-time Grand Slam champion Roger Federer.
Halep, the former world number two has missed opportunities to win a Grand Slam singles title, and she could have faced Williams in the final last year as the top two seeds but Williams lost to Roberta Vinci in three sets, and Halep was completely outplayed by eventual champion Flavia Pennetta in the semifinals.
The 22-time Grand Slam champion has been serving well throughout the tournament, and it appears that her shoulder problems have gone away, however, Williams has a bigger problem to deal with and that is to retain the world number one ranking.
Australian Open champion Angelique Kerber's fourth round victory over two-time Wimbledon champion Petra Kvitova means that Williams has to make the final to have any chance of keeping the world number one at the conclusion of this tournament.
Williams' route to the quarterfinals
The top seed has yet to drop a set throughout her 17th US Open campaign, and the American hasn't surrendered more than six games in an entire match, similar to her title run in 2014.
Williams easily dispatched two-time Grand Slam semifinalist Ekaterina Makarova in the first round, 6-3, 6-3 and she followed this up with a victory over compatriot Vania King with the same scoreline, although the world number one was erratic throughout this contest.
The six-time US Open champion played scintillating tennis in her first-day match in the Arthur Ashe Stadium thrashing Johanna Larsson 6-2, 6-1 in the third round, and she dropped only five games in her fourth round match with Yaroslava Shvedova which could have been a tricky affair, nonetheless, she advances to her 14th US Open quarterfinal with plenty in the tank.
Halep's route to the quarterfinals
Last year's semifinalist had a tough opener with 2013 semifinalist Kirsten Flipkens, however, it was a straightforward 6-0, 6-2 triumph for the Romanian and in the second round, Halep was up against unseeded lefty Lucie Safarova in the battle of the 2014 and 2015 runner-ups at Roland Garros.
The fifth seed got off to a dream start leading 3-0 but was pegged back at 3-3, however, Halep was able to weather the storm and defeat the Czech, 6-3, 6-4.
In the third round, Halep was involved in one of the women's matches of the tournament with Babos, but the Romanian dug deep after an underwhelming final two sets and defeated the hard-hitting Hungarian, 6-1, 2-6, 6-4 to advance to the fourth round.
Halep was paired with 11th seed Carla Suarez Navarro in the round of 16, and the Spaniard was a former quarterfinalist in New York back in 2013 and reached the Australian Open quarterfinals this year but it was a straight sets victory for the Romanian who progressed to the quarterfinals in Flushing Meadows for the second year in a row.
Their history
Williams and Halep have met on eight occasions, and the top seed has an overwhelming 7-1 head-to-head record in her favor.
Their first meeting was at a Grand Slam in the second round of Wimbledon in 2011, and the Romanian had the two-time defending champion on the ropes by attaining the first set, nonetheless, Williams stormed back to win the match 3-6, 6-2, 6-1.
The American thrashed the fifth seed in their second encounter in the semifinals in Rome on clay in 2013, 6-3, 6-0 en route to winning the title in the Eternal City. They met again later that year in the quarterfinals of the Western and Southern Open and once again, Williams handed Halep a bagel en route to winning the match 6-0, 6-4.
However, in their fourth meeting Halep registered her first win over Williams in the round-robin stage of the WTA Championships in 2014 thrashing the two-time defending champion 6-0, 6-2 but their fifth meeting would take place in the final of the WTA Championships, and Williams gained her revenge with a 6-3, 6-0 victory to win the title for the third consecutive year.
They met on two occasions in 2015 and they were due to meet in the semifinals in Indian Wells but the American was injured and withdrew, however, they met in the semifinals in Miami a few weeks later and it was one of the matches of the year with Williams taking it in three sets, 6-2, 4-6, 7-5.
Williams won their second meeting in 2015 in the final of the Western and Southern Open in straight sets, and the top seed ended Halep's title defense in Indian Wells in the process.
Who wins?
The top seed does not want to relinquish her world number one ranking, and she will do everything in her power to keep it, although it seemed unlikely at the start of the year that her position at the top would be threatened.
However, failing to defend her Australian Open and French Open points as the defending champion losing in finals to Kerber and Garbine Muguruza respectively, along with failing to defend her titles in Miami and Cincinnati, and playing a lighter schedule has meant that Kerber who has been having a consistent 2016 season is in the driving seat to take it.
Halep has been playing good tennis under the tutelage of Darren Cahill, and the Romanian may not match Williams power for power but she will be able to move the American around the court in uncomfortable positions as a counterpuncher.
On the other hand, Williams has been serving well throughout the tournament, and her serve could be a major factor in deciding the outcome of this match.
The fifth seed has a weak second serve which Williams will target with her powerful groundstroke returns, and if the six-time champion is fully focused, it should be another straightforward victory for her over Halep.
However, Halep is a good returner in her own right and if the American's serve is deserting her, the Romanian could take advantage of this with her punishing forehand on the baseline.
This quarterfinal match will be the first match of the night session in the Arthur Ashe Stadium, and the winner of this match will face a first-time Grand Slam semifinalist in the semifinals, either 10th seed Karolina Pliskova who won in Cincinnati this year and is riding a nine-match winning streak including a fourth round victory over Williams' sister Venus or 18-year-old Ana Konjuh who ousted fourth seed Agnieszka Radwanska in the previous round.
The crowd will firmly be behind Williams but the Romanian will have her fair share of supporters, and this contest between the duo should be entertaining for the crowd to watch.
Prediction: Williams in straight sets