Victoria Azarenka (1) vs. Angelique Kerber (7)
The world no.1 has reached this stage of the tournament through perspiration rather than inspiration. Azarenka put in a lot of effort to succeed at Wimbledon, and her quality of play at the Olympics so far has simply not been at the same level. However, being top of the ranking isn't always about playing fluent tennis but also grinding out victories in tough matches.
Angelique Kerber just goes from strength to strength, and it seems as if the German southpaw is now here to stay in the top ten of women's tennis. The most improved player on the circuit, Kerber showed a different facet of her game in her victory over Venus Williams. Displaying tremendous tenacity and spirit, Kerber came back from 5-1 down and 3-1 down to win both sets in tie-breaks. It could be a defining victory in Kerber's career.
With Azarenka looking patchy at best, and Kerber coming into the match with momentum and confidence, there is a genuine chance of an upset in this quarter-final.
Serena Williams (4) vs. Caroline Wozniaki (8)
It's as if Serena Williams never left Wimbledon. The serve is clicking with mechanical precision, the movement is fantastic, the ground-strokes are sizzling. Has there ever been such a dominant female player on grass? Her opponents seem resigned to lose even before a ball is hit in anger.
Caroline Wozniaki has done well to make it to the quarter-finals of the tournament. Grass clearly isn't her favourite surface, but the former world number one has hung in there with her trademark defence enabling her to defeat some tough opponents.
Wozniaki's defence won't be of much assistance against Serena however. Wozniaki is not going to be a factor in Serena's service games, while Serena will constantly attack Wozniaki's weak serve en route to another dominant win.
Kim Clijsters vs. Maria Sharapova (3)
You get the feeling that this match is between the only two players who at least stand a chance against Serena Williams on grass. In her farewell year Clijisters has not necessarily played her best tennis. However, the veteran seems to be relishing her last appearance at an Olympic tournament, and has progressed largely untroubled by playing some steady and consistent tennis against some tricky opponents.
Being the flag-bearer for Russia at the opening ceremony clearly meant a lot for Maria Sharapova. The French Open champion seems to be playing better than she did at Wimbledon. In the round of 16, she actually beat her vanquisher at Wimbledon Sabine Lisicki, using her experience to come back from a set down against an opponent who is always a handful on grass.
This match is simply too close to call. Clijsters has the ability to pounce on Sharapova's serve if it is not on song. However, if the match features long rallies, then Sharapova just might have the edge.
Petra Kvitova (6) vs. Maria Kirilenko (14)
After some frankly awful performances in the first two rounds, Kvitova gave all tennis fans a reminder of her grass-court pedigree in a thorough thrashing of Flavia Pennetta in the third round. Like Azarenka, Kvitova also seemed to suffer from a Wimbledon hangover, but finally seems to be back to her best.
Kirilenko continues to use her experience and crafty play to make it in to the deep end of tournaments. The relative veteran hasn't lost a set yet, and hasn't looked too troubled so far. However, she hasn't come across any heavy-hitters on grass, and that has certainly aided her progress.
Kirilenko will not give in easily, and she is guaranteed to give Kvitova a good tussle. However, Kvitova is in a different league on grass, and should come through against Kirilenko in straight sets.