After only two games, there is very little to be gleaned from most of the statistics for the Cardinals thus far. The Cardinals' .129 batting average means about as much as their 0.52 ERA which only means slightly less than a 1-1 record after two games. The most important thing at this point in the season is that nobody has been injured. After that, it might be interesting to examine lineups, debate bullpen usage, and continue the roster construction debate that has gone on since the Cardinals' season ended last fall. Looking just at the first two games, the most encouraging single aspect for the Cardinals has been the starters ability to pitch deep into games.
Thanks to Michael Wacha and Adam Wainwright, the Cardinals bullpen has yet to be called upon with more than seven outs to go in a typical nine-inning game. While Cardinals starters will not continue to average nearly seven innings per start, racking up innings to save the bullpen will likely be very important. Heading into the season, the Cardinals appear to have average to above-average players at every position, a strong rotation, a decent bench with reinforcements from Triple-A if they need it, and a very strong back end of the bullpen. Where the Cardinals appear to be weakest, highlighted by a spring training of disappointing options that led to bringing David Aardsma to camp after his release by the Indians, is middle relief.
For any team, lacking strong middle relief is not a good problem to have, but not as bad as other, more potentially pressing issues in the rotation and lineup. The easy way to ensure middle relief is not pitching important outs has been used effectively over the first few games: avoidance. The Cardinals have gotten outs out of their bullpen from just three pitchers: Kevin Siegrist, Carlos Martinez, and Trevor Rosenthal. In both games, they have been able to use their bullpen without calling upon Seth Maness or Keith Butler. Maness pitched well last year by walking just 1.89 hitters per nine innings and inducing groundballs 68.4% of the time. He can still be effective pitching the same way, but if he is only striking out a shade over five hitters per nine innings (14.1 K%), it will be difficult to reproduce the same results this season. Butler won his spot by default, aiding his cause by already having a place on the 40-man roster.
Avoiding middle relievers impacts a bullpen's ability to limit runs. In an article about whether or not complete games produce an extra effect beyond limiting bullpen innings(they don't), Russell Carleton looked($) at situations where a manager could use his optimal bullpen. One such situation is when there is no game the next day. The manager is less constrained with overworking his bullpen with a guaranteed day off and likely uses his best relievers. In those situations, the average runs allowed (not to be confused with ERA, as it includes runs from errors as well) is 4.15 compared to 4.42 when there is no day off following the game. When teams use their best relievers, the team performs better.
The above principle is also highlighted by the work of Colin Wyers($), cited in Carleton's link. Wyers examined bullpen performance and found the deeper a pitcher went into the game, the better his bullpen performed.
At about 6 IP (roughly the average duration of a start) you see a relief RA of 4.42, while relievers in that time span had an average RA of about 4.52. And if you can really go deep into the game and give seven or eight innings of solid performance, you can get solidly above-average relief support.
At seven innings the averaged runs allowed was around four while at eight innings and beyond the average moved another half-run to run lower depending on the number of outs in the inning. Granted, some of the relief innings earlier in games are likely to be low leverage situations where only mop-up duty is required. However, even the Cardinals' best relievers will only be pitching every other game, potentially leaving important sixth and seventh inning outs to Maness and Butler.
Last year, the bullpen was called upon for 475 ⅓ innings pitched. The Cardinals ranked third among National League team in innings per start at 6.08 compared to the league average of 5.91, essentially getting an extra out every other game. Starters will need to continue their success and perhaps improve on it to limit middle relief innings. If Rosenthal get another 80 innings, Siegrist and some combo of Martinez and Joe Kelly can get another 130, Neshek and Choate combine for about 75 (Ben did a good job summing up the dangers of having two OOGYs here), that still leaves another 200 innings, some of those likely to be very important innings. Despite Ben's protest, the Cardinals added Neshek to the bullpen, creating more innings for the potential middle relievers in what could amount to high leverage situations. With Neshek likely only a one out pitcher, every inning a starter can take away from a middle reliever could prove very valuable to the Cardinals.
With his innings cap off, Shelby Miller should improve on his 5.59 innings per start. Including playoffs, Wacha averaged 6.05 innings per start. Lance Lynn was also above six innings per start last season while only three pitchers (Chris Sale, Cliff Lee, Clayton Kershaw) exceeded Wainwright's average of 7.11. Even Joe Kelly's 5.8 average is not bad for a fifth starter. The Cardinals' starters will need to pitch well to mask their current deficiency in the sixth and, on some days, the seventh inning.
Even without improvement or perhaps a little lightening of Wainwright's load, there are other scenarios that could lessen this concern. Motte coming back strong would add another prominent late-inning reliever. If Garcia came back and pushed Kelly to the bullpen there would be little concern at all, but the best case scenario is not the most likely scenario. All fans have times they see a pitcher struggling, they look down at the bullpen and cringe. The Cardinals' middle relief has not presented itself as an issue thus far due to tremendous starts from Wainwright and Wacha (an argument could be made Rosenthal pitches the ninth inning last night if Matheny had more confidence in his middle relievers, but I'm not going to get into that here). Limiting exposure is the best way to make a bullpen at its most effective. The Cardinals' rotation definitely has the ability to do so, potentially preventing a problem before it can begin.