It's nearly impossible to separate Roger Federer and Andy Murray at this point in each of their brilliant tennis careers. Sure, Fed has the resume, but Murray is six years younger and has lots of championship moments still ahead of him.
Perhaps this November in London will announce a changing of the guard in men's tennis. While Federer is ranked No. 2 in the world, Murray is right behind at No. 3. Is this the tournament that declares Murray the second-best player on the planet? Or the one that ensures another year of Swiss dominance?
Answers to those questions will have to wait. But for now, let's break down the biggest keys to Sunday's must-see ATP World Tour Finals semifinal matchup between Federer and Murray.
Beating the game's best requires a player to find early success in his service games. For both Roger Federer and Andy Murray on Sunday, putting their first serves in play will be crucial to keeping their opponent on his heels.
In addition to putting the ball in play early, the advantage will go to the player who finds the most success on his first serve. Just take a look at what Juan Martin del Potro did against Roger Federer on Saturday. The Argentine won 81 percent of his first-serve points. That's impressive when you consider that Fed's previous two opponents, David Ferrer and Janko Tipsarevic, won just 69 and 56 percent of their first-serve points respectively.
In Murray's loss to Novak Djokovic on Wednesday, the Scot won just 71 percent of his first serve points. The key to winning on Sunday will be putting the ball in play quickly in the service game and then making sure to capitalize. Look for Sunday's semifinal winner to have won around 80 percent of his first-serve points.
Capitalize on Break Points
Break points are very difficult to come by when you pit two of the world's best head-to-head. But whenever Murray or Federer comes across an opportunity to break, they will absolutely have to capitalize in order to win.
In Murray's narrow loss to Djokovic earlier in the week, he only cashed in on two of seven break-point chances, while his opponent won three of seven and ultimately the match. In Federer's loss to del Potro on Saturday, he won just 25 percent (1-of-4) of his break-point chances, while del Potro won his only break-point opportunity.
The player that makes the most of his break-point chances will surely be moving on to Monday's final in London.
Focus and Stamina
Tennis, more so than any other sport, demands a constant focus and ability to take the match one point at a time. That's why only a few players in the world can fight back from one or even two sets down to win.
In Sunday's semifinal matchup, though, it's hard to say whether one player, Murray or Federer, has a distinct advantage in this area.
While Federer's focus is among the best ever witnessed (he has 17 Grand Slam titles to show for it), Murray has the advantage of an extra day of rest, having only played two sets in his most recent match. Therefore, the stamina edge would have to go to the younger, fresher Murray.
So, here we are, back to square one. There's simply no separating these two men in 2012. They've each won a Grand Slam, Fed has the better singles record (68-10) and Murray has the Olympic gold. There's no telling who will come out on top, but what we do know is that the winner will have to hit on all three of these match keys in order to make the final.
Follow Bleacher Report Featured Columnist Patrick Clarke on Twitter.