After last night's 14-inning affair, the Yankee bullpen has a 4.11 ERA in 28 games. In 92.0 total relief innings pitched, they've given up 42 earned runs. By that measure, they fall in the lower half of MLB bullpens. When you look at how those runs have been given up and by whom, however, the performance of the 'pen starts to look better.
In 13.2 combined IP, the group of Bruce Billings, Vidal Nuno, Chris Leroux, Matt Daley, Cesar Cabral, and Dean Anna have allowed 25 of the 42 ER. By comparison, the group of David Robertson, Shawn Kelley, Adam Warren, Matt Thornton, and Dellin Betances have combined to give up 11 ER in 59.2 IP. The core of the Yankee bullpen has been very, very good from day 1. It's the back end that's been the weak link, something that shouldn't come as a shock considering David Phelps and Nuno have moved into the rotation. That dynamic played out in textbook fashion last night, when the core group of relievers gave up 1 ER in 8 innings of work and Leroux gave up 5 in 1.
In short, the Yankees have a good enough bullpen to compete and succeed in the AL East. They just need some help shoring up those last few spots so they don't get exposed in extra-inning games.