Last year, the Toronto Blue Jays were supposed to be contenders.

They were crowned the winners of the offseason after acquiring Josh Johnson, Jose Reyes, Mark Buehrle, R.A. Dickey, and Melky Cabrera in the same winter, giving their roster a big boost on paper. On the field, though, it didn’t work.

Johnson was lousy and injured, while Buehrle and Dickey failed to improve the rotation much even though they avoided the DL. Reyes and Cabrera both struggled with injury issues of their own, with Cabrera performing as one of the worst players in baseball when he did play. Instead of joining the A’s, Indians and Pirates in the "Postseason of the Upstarts," the 2013 Blue Jays instead became another reminder of the perils of trying to build a team around splashy, big-name acquisitions.

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Coming off a miserable season, the Blue Jays backed off from aggressive offseason upgrades. They signed one free agent to a major-league contract: Dioner Navarro, a part-time catcher signed for part-time money. Despite being linked to big names like Jeff Samardzija, the team’s most notable trade involved reliever Brad Lincoln going to Philadelphia for backup catcher Erik Kratz. Basically, the Blue Jays stood pat, despite what looked to be glaring holes in the rotation and at second base, not to mention all the questions about the big-names who disappointed so dramatically a year ago.

Put it all together, and you have a last-place team that made no substantial upgrades over the winter, built around a core group of players that are almost universally on the wrong side of 30. That’s not a classic recipe for success, but as we head towards June, the Blue Jays are alone atop the American League East, and they now look like the prohibitive favorites to win the division.

How did the Blue Jays fix themselves by doing nothing? There are two primary, obvious differences between this year’s model and last year’s version.

1. The 2013 Blue Jays sent a position player to the plate 6,125 times, and 1,881 of those — a whopping 31 percent — went to players who performed below replacement level on the season. Maicer Izturis was the chief offender, posting an MLB-worst -2.1 WAR on the season, meaning that the Blue Jays would have been two wins better had Iztruis been replaced by a generic Triple-A infielder. Izturis wasn’t alone, however; along with Cabrera, J.P. Arencibia, Josh Thole, Emilio Bonifacio, Anthony Gose, Henry Blanco, and Andy LaRoche, the Blue Jays had eight players combine for a whopping -5.1 WAR.

This year, only 286 of the team’s 1,980 plate appearances by position players — only 14 percent, less than half of last year’s rate — have been given to players who currently have a negative WAR, and those five players have combined for just -1.0 WAR. One of those five players — center fielder Colby Rasmus — was among the team’s best players last year, and has a track record that suggests he won’t keep performing this poorly all year. If he improves as expected, the team is only really giving away at-bats at second base, and that’s the kind of weakness that can be improved at the trade deadline.

Last year, the Blue Jays gave away three full-time players’ worth of at-bats to below replacement level performances. While there’s a heavy emphasis on the top of a team’s roster when projecting future performances, the Blue Jays are a great reminder that avoiding terrible performances from the end of the roster is just as important.

2. Their starting pitching has stopped giving up home runs. The debacle that was their 2013 rotation was due in large part to a ridiculous rate of home run allowance: 1.36 homers-per-nine-innings, second worst in baseball. This year, that rate is just 0.82 HR/9, sixth best in baseball. And that single change is driving the entirety of the one-run decrease in their rotation ERA. See for yourself.

The strikeouts are essentially the same, while the walks are actually up a lot, which isn’t a great sign, but the increase in walk rate is dwarfed by the decrease in home runs allowed. By measures of expected performance, Toronto’s rotation hasn’t really been that much better this year than it was a year ago, but the huge change in homers allowed has driven its ERA way down, and allowed the team to remain competitive.

The problem for the Blue Jays is that the 4.35 xFIP is more representative of what they should expect from their starters over the rest of the year, as the 3.75 ERA is a bit of a mirage. While the 2013 Blue Jays were certainly underachievers, the 2014 Blue Jays are likely overachieving, with some regression almost certain to come from the team’s starting rotation.

But even with that coming regression, the Blue Jays still have to be considered the favorites to take the AL East. The division isn’t the behemoth it once was, and supposed-to-be contenders in Tampa Bay and Boston have dug themselves holes large enough to make comebacks difficult. The Yankees and Orioles aren’t anything special, and the Blue Jays’ early lead gives them a leg up on both. As it currently stands, the FanGraphs Playoff Odds projection has the Blue Jays winning the division with an 87-75 record, and no other team in the division finishing better than 82-80. Even if the Blue Jays just play .500 ball the rest of the year, their 31-22 start should be enough to give them a real chance to win the division.

But the time for sitting by and letting positive regression work its magic has come and gone. With the expectation of contention comes a requirement to upgrade when possible, and no contender in baseball has a more obvious weakness than the Blue Jays have at second base. They could use another starting pitcher, but fixing the second base hole should be priority No. 1.