The Orioles are five games up in the East, the biggest division lead in the American League. How in the world are they doing it?
Part of it is Baltimore's defense; they can't really be given credit for having Matt Wieters behind the plate this year due to how long he's been injured, though he is one of the game's better defenders. But the team does have one of the best infield defenses in baseball, especially on the left side -- J.J. Hardy and Manny Machado are the best shortstop-third baseman combination in the game, with Elvis Andrus/Adrian Beltre in Texas and Troy Tulowitzki/Nolan Arenado in Colorado being the only other pairings that come reasonably close. (Side note: if the Yankees actually make the necessary re-signings to sustain a Mark Teixiera/Stephen Drew/Brendan Ryan/Chase Headley infield next year, they'll be one of the best foursomes in the league in this regard, but not quite yet.)
The Baltimore outfield isn't full of world-beaters -- both Adam Jones and Nick Markakis are overrated at their respective positions in center and right -- but outside of Nelson Cruz and the occasional Delmon Young adventure, it is a quality unit. The same can be said of current catching tandem of Caleb Joseph and Nick Hundley, with the caveat that Joseph has shown himself to be a very good pitch framer in his short time in MLB, if that's something you go in for; I'm still undecided.
Then there is Baltimore's rotation, which is at best unconventional for a leader in what was supposed to be one of the toughest divisions in baseball: Six pitchers have started over ten games for the Orioles this year, and their ERA (ERA+) range from Bud Norris's 3.68 (105) at best to Ubaldo Jimenez's 4.52 (86) at worst. Jimenez is the outlier though: Chris Tillman's 3.78 (102), Kevin Gausman's 3.77 (103), Wei-Yin Chen's 3.90 (99) and Miguel Gonzalez's 3.93 (99) all skew closer to Norris than Jimenez in terms of performance. Given that MLB's average performance for a starting pitcher this year is a 3.90 ERA (without adjusting for park, and the Orioles play in a hitter-friendly one), having a slightly above average MLB starter on the mound every night can, in aggregate and with the proper support, be just as beneficial as a top-heavy rotation like Philadelphia's or, at the moment, Anaheim's, or even the Dodger rotation now that Roberto Hernandez and Dan Haren make up the backend.
The Orioles, of course, do not win games through pitching alone. But then, they're not quite having a stellar season at the plate, either: only a .722 team OPS against a league-average .705, and only one full-time player -- Cruz -- having a season at the plate worth remarking on, with an .836 OPS (131 OPS+). Both Steve Pearce and Delmon Young are having similarly good seasons, but the fact that all three players share similar skill sets -- right-handed power bats with minimal defensive utility anywhere but left field -- has caused a bottleneck for playing time. Overall, the Orioles are simply not that impressive a team. So how have they won 65 games?
Good bullpen, good luck, bad division and close games. Their bullpen is having a great year (even if it is not a particularly deep pen) and they're 23-17 in one run games. In addition, the Orioles are 12-4 in extra inning contests. Not quite the ridiculously lopsided split of the 2012 Orioles in late and close situations (that squad went a mind-boggling 29-9 and 16-2 in those situations, respectively), but still pretty decent, especially in the extra innings format.
And it's hard to understate how much the Orioles have benefitted from being the only truly healthy team in the division. The Wieters injury was a loss, sure, but Caleb Joseph has been more than adequate behind the plate replacing him (which is odd, and possibly unsustainable, because as noted in the link above, one of the biggest knocks on Joseph coming up was his defensive game), and he is the only major loss for the Baltimore team. Meanwhile, the Blue Jays are playing without Edwin Encarnacion, Adam Lind, Brandon Morrow or Brett Lawrie, and the Yankees rotation has been an ongoing mess that's just now stabilizing a bit.
So long as that situation continues and the Orioles' only real threats in the division are incomplete versions of the Yankees or the Blue Jays, and so long as Baltimore don't themselves suffer any critical injuries, the O's should have a very good chance of making the postseason for the second time in three years. But of course getting to the playoffs is very different from succeeding there, and it's quite likely the magic that Baltimore's counting on to get them through September will be quite ineffective in everything after.