In 2012 the Washington Nationals entered the seventh inning with a lead 88 times, ended the inning 86 times with the lead, and won 82 of those ballgames. The 2012 Nats in total had a 93% chance to win a ballgame when they entered the seventh inning with a lead. For comparisons sake the average MLB team had an 88% chance to win when entering the seventh with a lead. The Nats in 2012 were 5% better at winning games when they had the lead in the seventh while they were 0.3% better at winning with a lead in the eighth and 1.6% better at winning with a lead in the ninth. The key to a Nats victory in 2012 was the seventh inning.
Why were the Nats so good at getting through the seventh? The Nats entered the inning with a lead 88 total times and not once did that inning end with the Nationals behind. The first and most important aspect is that the Nationals had the lead. In 2012 the Nationals had the fifth best offense in the NL scoring 731 runs. The Nationals were the fifth best team at scoring runs, but they were also the second best team in the NL at preventing runs, and the best at doing so with their starting pitching. The Nats starters led the NL with an ERA of 3.40.
While we are focusing on the Nats extreme success in the seventh inning with the lead it is important to understand how they got there and of the 162 sixth innings the Nationals played in 2012. Starters pitched 114 of them. Compare that to a seventh inning that saw the starters innings drop from 114 down to 51 1/3. In fact in games in which the Nationals starters failed to finish the sixth inning the Nationals were 23-35, and an even worse when they failed to even make it to the sixth. The Nationals were able to get to the seventh with a lead 88 times, because they had an offense that could put runners across home plate, and a pitching staff and defense that could prevent the other team from doing so.
With the Nationals starters only pitching 51 1/3 innings in the seventh it was largely an inning for the bullpen with the bullpen pitching 68% of the seventh innings the Nationals played in 2012. It is important to keep in mind that almost nothing went according to plan with the Nationals bullpen in 2012. Drew Storen spent most of the season on the DL and Henry Rodriguez and Brad Lidge under preformed badly, forcing Tyler Clippard into the ninth and Sean Burnett into the eighth. Even with the disarray the Nationals bullpen was deep enough that for most of the season they had a primary closer and a primary set-up man. It would then be a worthy assumption that the seventh inning would be a match-ups inning. Meaning that Mike Gonzalez would have near as many appearances as Ryan Mattheus and Craig Stammen, but that is far from the case.
The top five Nationals to make appearances in the seventh are Ryan Mattheus (35), Craig Stammen (34), Tom Gorzelanny (22), Edwin Jackson (15), and Gio Gonzalez, Jordan Zimmermann, and Mike Gonzalez tied for fifth with 14. Judging by innings pitched and the order changes to Stammen (28 2/3), Mattheus (28 1/3), Gorzelanny (20), Jackson (13 1/3), and Gio Gonzalez (12). Mike Gonzalez is tied in appearances with two starters, but only managed to pitch 8 2/3 innings in the seventh and 8 of his 14 appearances in the seventh came with runners already on base. Mike Gonzalez wasn't used as a match-up LOOGY in the seventh. He was used as a cleaning-up a mess LOOGY. The primary pitcher with a lead in the seventh was Ryan Mattheus. Of all his 66 appearances Mattheus pitched 41 of them with a tie or lead primarily in the seventh and averaged three outs an appearance, the third highest total for a reliever on the Nats behind only Craig Stammen and Tom Gorzelanny, the long relievers.
There is one final piece of the puzzle to all this. In 2012 the Nationals had a team WHIP of 1.221 meaning that on average they allowed 7 to 8 base runners before the seventh inning. What that means is that while the numbers indicate that Ryan Mattheus was trusted with this important inning and that because of it the Nationals were able to win a lot of games that might not be the case. By allowing between 7-8 base runners in innings 1-6 the most common parts of the opposing batting order to bat in the seventh would be either 8-9-1 or 9-1-2, and many managers opt to put speed or contact hitters at the top of the order whomever pitched the seventh for the Nats wasn't facing the heart of the order. Those players were more often at bat in the eighth or ninth inning where the Nationals weren't that much better than league average at preserving a win.
All of that is great for 2012, but what does it mean for 2013. As discussed previously the most important part of winning games is having a lead, and by adding OBP through Denard Span at the top of the order and with more playing time for Harper, Werth, and Ramos the 2013 Nats should score more runs than the 2012 Nats. Using Bill James projections for wRC for the Nats expected 25 man roster the 2013 season is projected to score 779 runs. That may be a bit on the optimistic side considering the best offense in the NL last season were the Brewers who score 776 runs. 779 isn't unbelievable, but it is likely the ceiling for the 2013 Nationals. The 2013 Nationals should score more than the 2012 Nats, but they probably won't be the best offense in the NL.
The other important part is the starters. In 2012 Nationals starters pitched 70% of the sixth innings played, and averaged 5.9 innings pitched a game. In 2012 Jordan Zimmermann had 20 starts between 80 and 99 pitches and many times was removed from games while he still looked fresh. The Stephen Strasburg innings limit was more widely publicized, but Jordan Zimmermann was on a limit himself even though it was a less apparent one. Even if Strasburg is on a similar restriction as Jordan Zimmermann was in 2012 in 2013 he is going to start more games and will be allowed to throw more pitches. Of the Nats top three pitchers Strasburg averaged the fewest pitches per outing at 93. With that allowed to increase to the 97 Jordan Zimmermann averaged in 2012 and the 5 or 6 extra starts the Nationals starters will be well on their way to averaging over six innings a game. Substitute Dan Haren for Edwin Jackson and it should be a lock that the Nationals average more innings pitched per start in 2013 than 2012.
The final piece of the puzzle for all this is the bullpen. If the Nationals are as good at preventing base runners as they were in 2012 it won't matter all that much who pitches the seventh. Mattheus could very well lead the team in appearances in the seventh once again while Clippard and Soriano, and Stammen and Storen are paired off as an A and B bullpen, or Davey Johnson could go with Clippard, Storen, Soriano as the back three for most of the season, or the two philosophies could flip flop depending on how many days in a row the relievers have pitched.
The Nationals have a deep bullpen and Davey Johnson is going to have many options as to how to use it. On paper the Nationals head into 2013 with a better offense, rotation, and bullpen than they had 2012, and in 2012 the Nationals were 5% better than MLB average at preserving wins when they entered the seventh with the lead. Still the fact remains that while the Nats were 5% better in the seventh they weren't any better in the eighth and only 1.6% better at preserving wins in the ninth. That kind of success may not even be able to be duplicated let alone improved upon.