I started with the National League (here, here, and here), the AL West, and the AL Central. So this is it.
Boston Red Sox, 97-65: Maybe it's me, but the Red Sox going from worst to first last season didn't get all the fanfare it might've. Probably nobody really believed it was a last place club to start out with.
What changed? Well, when you score 119 more runs and give up 150 fewer from one season to the next, good things happen. But what caused those improvements? Let me point to two less obvious things. On offense, the team had 153 more walks, almost one per game, going from second-to-last in the AL to second. Only two players on the 2012 team got 40 walks. In 2013, there were eight. That's a lot of baserunners. As for pitching, it was a story of the starters, whose ERA fell from 5.19 in 2012 to 3.70 in 2013, largely because of a lot more strikeouts (18% higher rate of strikeouts per plate appearance) and a lot fewer home runs (21% lower rate per batter).
Tampa Bay Rays, 92-71: The Rays play their home games at Tropicana Field, a pitchers' park. Even though they had a decent offense last year, as evidenced by their sixth-best OPS in the league in road games, they scored only a league-average 4.3 runs per game. That meant their pitchers had to rely on limited run support. In games in which the offense supplied scored 3-5 runs, the average American League team went 21-18 with a 3.99 ERA. The Rays pitchers flourished, leading the league with a 32-12 record and a 2.77 ERA. The next best team, the Red Sox, had a winning percentage 127 points lower and an ERA 0.62 runs higher when receiving 3-5 runs of support.
Baltimore Orioles, 85-77: Skeptical about my Yankees comment? Just look at the Orioles. In 2012, somewhat famously, they had a 29-9 record in one-run games, the best in the majors. Some pointed to the team's strong bullpen and winning attitude, while detractors attributed it to luck. The skeptics won out, as last year, the team's one-run record swung to 20-31, the worst in the league. (Actually, the Astros, at 18-36 were worse, but given that their winning percentage in one-run games, .333, was better than their record in other games, .306, you can't really say they were unlucky.) If the O's can split the difference and play .500 ball in one-run games this year, they'll have a better record, if not a better narrative.
Toronto Blue Jays, 74-88: The Jays were probably the most disappointing team in the league last year. After big moves in the offseason to add Jose Reyes, Melky Cabrera, Mark Buehrle, Josh Johnson, and defending NL Cy Young winner R.A. Dickey, they were picked by some to win the division. Instead, they improved by only one game from 2012, finishing in last with a 74-88 record, done in by defense (fourth-most errors in the league), pitching (third-most runs allowed), and injuries. Only the offense, which scored more runs per game (4.40) than average (4.33), was OK.
Except at second base. The worst-hitting position in the American League was Toronto's second base. Blue Jays keystoners managed just a .216/.258/.297 slash line. How bad is that? Three pitchers (minimum 50 plate appearances) had a higher batting average, on base percentage, and slugging percentage.