Roger Federer (1) vs. John Isner (10)
The king of grass is clearly relishing participating at the Olympics on his domain at Wimbledon. While all the remaining quarter-finalists have struggled with the inconsistencies of the grass compared to Wimbledon, Federer has once again proved his adaptability to play on tricky surfaces without compromising his flair and guile. After a tricky opening round match against Alejandro Falla, Federer has stepped up his game, ruthlessly defeating Julien Benneteau and Denis Istomin.
John Isner plays in a manner similar to Istomin, with the key difference being a better serve. The marathon man has not necessarily played his best tennis, but his serve has helped him stay afloat in tight matches, and he will have to rely on it firing on all cylinders against Federer.
Isner does have the confidence gained by beating Federer earlier this year in Davis Cup action. However, Federer on grass is a completely different proposition. The Swiss maestro is bound to trouble Isner by keeping the ball low, and for all Isner's prowess with the serve, Isner himself is hardly going to get a look on Federer's serve. Isner might take a tie-break, but Federer should ultimately prevail.
Kei Nishikori (15) vs. Juan Martin Del Potro (8)
Many have been waiting for Kei Nishikori to reach the higher echelons of the game, and the talented Japanese player has finally had a breakthrough year. After reaching the quarterfinals at the Australian Open, this is Nishikori's second major quarter-final appearance of the year. Nishikori has had to come through some tough encounters on his least favourite surface. Nonetheless the way he took the first set 6-0 against David Ferrer hints at his potential.
Another player who doesn't necessarily enjoy playing on grass is Juan Martin Del Potro. The Argentine has mixed some brilliant tennis from the baseline with phases of erratic play. Other than a slight wobble against Giles Simon in the previous round, Del Potro has looked in decent control throughout the opening rounds.
Del Potro should ideally have too much in store for Nishikori on grass. However, there have been plenty of recent examples of Del Potro imploding against players like Nishikori who are adept at absorbing his power and frustrating him in long rallies. If Nishikori succeeds in his game plan, an upset is viable.
Nicolas Almagro (11) vs. Andy Murray (3)
It certainly is a mystery as to why Nicolas Almagro hasn't had better results at Wimbledon and on grass in general. Almagro has used his excellent serve and whip-like backhand to great effect at the Olympics so far. He hasn't looked like losing a set and has displayed some rarely seen deft touches as well.
Andy Murray has played some outstanding tennis so far in the tournament. It seems remarkable that Murray seems to have drawn out even more fervour and passionate support at the Olympics compared to Wimbledon. Other than a slight hiccup against Marcos Baghdatis in the previous round, Murray has been playing some serene tennis, mixing his brilliant movement with subtle slices and drop shots to outfox his opponents.
Almagro might have the more potent serve, but against the best returner in the game that weapon will be neutralized. With his all-court game and tactical acumen, Murray should progress in straight sets.
Jo-Wilfried Tsonga (5) vs. Novak Djokovic (2)
That Tsonga was able to come on court the very next day after his 4 hour marathon victory against Milos Raonic, and then defeat Feliciano Lopez in straight sets, proves he has now added the mental toughness and desire to win that has established him as the best player behind the big 4. As usual the tennis has been sublime mixed with the ridiculous from the Frenchman.
Novak Djokovic has flown slightly under the radar at this event, as the whole world is hoping for another Murray-Federer final. Djokovic hasn't looked at his best, coming through a war of attrition against Lleyton Hewitt in the last round, a match for the most part he looked like losing. Once he saved the second set, his athleticism and fitness came to the fore, allowing him to unleash his vast array of strokes.
Tsonga is always in with a chance against anyone on grass, however Djokovic has got the better of him recently. One feels that Tsonga might not have the belief during the crucial moments to get the better of Djokovic. Djokovic might lose a set, but will end up booking a place in the semis after an extremely close battle.