Federer was the last player to beat Djokovic on a major stage. His four-set victory over Djokovic in last year's French Open semifinal must serve as a blueprint in this year's contest.
Both players are coming off of quarterfinal scares. Federer was taken down to the wire by Juan Martin del Potro, and Djokovic was tested by Jo-Wilfried Tsonga.
This is the semifinal match everyone was waiting for. Predictably, it has arrived.
Let's take a look at how Federer can keep Djokovic from winning his fourth straight Grand Slam competition.
Federer broke Djokovic's serve four times at Roland Garros last year. He will need to do the same, or better, this time around.
Breaking a serve not only earns points, but it steals momentum. Tennis is an extremely emotional sport, and losing a critical serve can prove pivotal to the rest of the match.
Federer must play strong on the baseline and make sure Djokovic doesn't get anything easy. In last year's French matchup, Djokovic landed 67 percent of his first serves.
Holding the baseline and playing tough on Djokovic's first serve will allow Federer to take advantage of second serves. These will not be as unpredictable and should be easier to return.
At this point, Djokovic moves much better than Federer. He must counter this by winning his own serve and breaking Djokovic's dangerous services.
Control the Net
If Federer controls the net, he will keep Djokovic from becoming the first player since Rod Laver to win four straight Grand Slam titles.
Federer's accuracy, touch and graceful play has aged well. He has a feathery touch and is agile enough to attack the net with calculated confidence.
Playing toward the net will ideally keep Federer from playing Djokovic in a match centering around long volleys. Federer cannot keep up with Djokovic in this playing style.
Charging the net and forcing Djokovic to play a finesse game counters his conditioning and age advantage.
Federer must use the net to his advantage without using it exclusively.
Force Him Back
Djokovic struggles against players who hit the ball deep. Federer must keep him back on his heels and make him swing upwards at the ball.
This will make Djokovic less accurate and give Federer time to react toward the next shot.
Federer must pound the baseline on Friday. Keeping shots on the baseline will not allow Djokovic to knock short shots with his howitzer-like forehand and precise backhand.
If Federer plays predictable and gives Djokovic a series of short shots, it will be a long day. Djokovic is extremely well-conditioned, very powerful and in the height of his career.
Using tactful shots to keep Djokovic off balance is Federer's best chance at advancing to the French Open finals.