Group A consisted of Roger Federer, Andy Murray, Juan Martin del Potro, and Fernando Verdasco.  With 3 Slams won by members of this group, Group A was considered the tougher group.

Today was the last day of the round robin for Group A and the results came down to the wire.  Andy Murray played earlier in the day and needed three tight sets to beat Fernando Verdasco.  Although Murray held serve fairly easily for many games, and although Verdasco had many break points against him, Murray couldn’t find a way to convert.

Murray was pushed to a third-set tiebreak and finally emerged victorious: 6-4, 6-7 (4), 7-6 (3).  However, it turned out that this tight match was Murray’s undoing.

With this victory, Murray had a 2-1 record.  With the final match between Federer and del Potro yet to be played, Federer was comfortably up 2-0 and del Potro was 1-1.  If Federer won, both he and Murray would have the two best records, and both be in the semifinals.

However, if Federer lost, other tiebreak rules would go in effect because each of the top 3 players would have a 2-1 record.  If Federer lost in straight sets, then del Potro would have a 2-1 record, but have lost the fewest sets since the remaining matches were all played to 3 sets.  In this scenario, Federer would be out of the semifinals because he would have won fewer sets than Murray (since Murray won at least 1 set in each of his matches).

If Federer lost in 3 sets, then, each of the three players (Federer, Murray, del Potro) would have won and lost the same number of sets and the tiebreak would then be percentage of games won, i.e., total games won/total games played.

Federer lost the first set easily to del Potro who seemed to be hitting with his US Open form.  Federer played a very close second set that eventually went to a tiebreak.  del Potro got up early, but then Federer got back on serve, before del Potro again took a point of Federer’s serve and had chances to serve out the set and ensure Murray get to the finals.  Only del Potro lost 2 points on his serve, and Federer closed out the second set.

At 3-all, Federer had chances to break del Potro, at 15-40.  del Potro extricated himself out of that game and held for 4-3.  Federer then played a sloppy game to go down 0-40 and del Potro eventually broke to go up 5-3.  del Potro then closed out the match and won the third set, 6-3.

With win-loss as the tiebreak, Federer ended up having the best win-loss percentage.  It didn’t hurt that he had two 6-1 sets, one against Verdasco and one against Murray.  Meanwhile, del Potro had won one more game than Murray but had the same losses, so del Potro had a better win-loss but just barely.

In Group B, Djokovic will play Nadal.  Nadal has already been eliminated because he has a 0-2 record and everyone else has 1 win.  If Nadal beats Djokovic, both will be 1-2.  However, Nadal would have 2 sets won and 4 sets lost.  If Djokovic loses in straight sets, he will also be 1-2 with 2 sets won and 4 sets lost, but Davydenko would have 3 sets won and 4 sets lost in the worst case (2 sets won over Nadal, 1 set with Djokovic, and assuming a straight set loss to Soderling) and he and Soderling would get in based a hypothetical Soderling straight set win.

If Soderling loses and Djokovic loses, then Soderling is 2-1, Davydenko is 2-1, and both Djokovic and Nadal are 1-2 and are out.  If Nadal loses and Soderling loses, then Djokovic, Soderling, and Davydenko are all 2-1 and set percentage will apply.  Currently, Soderling is 4-0, Djokovic is 3-4, Davydenko is 3-4.  Soderling should get in because he will only lose 2 more sets at worst.  At that point, it will be a matter of how well Djokovic or Davydenko win their matches.  Djokovic has a better chance, given his recent win over Nadal, than Davydenko who has recently lost to Soderling.

The ATP World Tour Finals is nearing conclusion with half the players in the semifinals set, and the other half still up in the air.  One more day of round robin play to decide that half!