To win your fantasy league, working the waiver wire is essential. There's no way around it. You might've had the perfect draft, and it'll all go down the drain if you let your opponents snap up all the goodies in free agency, or don't adequately replace your injured studs.

That's what we're discussing here. All injuries are not created equal. If you have a starting pitcher whose going to miss a week, a different free agent may be appropriate than if you've lost a guy for half the season. That said, here are the types of guys you should be targeting off the bat.

Replacing the star pitcher in the short term (Ex. Cole Hamels, Taijuan Walker)

Hamels is obviously more established than Taijuan Walker of the Mariners, but if Walker's hype comes true right away then the upside is about the same. Both guys are expected back by the end of April, so feel free to take a stab on riskier pitchers with higher upside whose rotation spots aren't guaranteed.

Brett Anderson, SP Colorado Rockies (Ownership: 14.1 percent)

Anderson is a known injury risk, but guess what? He's not hurt yet. Anderson's stuff is filthy so ignore the fact that he's pitching in Colorado. He is an ace that doesn't get paid like one or trusted as one because he's a lock to get injured at some point. Even last year's crappy numbers are lying--yes, he had a 6.08 ERA and a 1-4 record, but his FIP was a 3.85 while he struck out more than a batter per inning. For the rest of April, he could easily give you Hamels numbers, then you ride him until he dies out. If you're lucky you'll get some time with both in your rotation.

Jenrry Mejia, SP New York Mets (Ownership: 29 percent)

The Mets play in a pitcher's park (CitiField) and Mejia has fantastic stuff. He's the announced fifth starter this season and will almost certainly have a low and strict innings limit. That said, you'll probably only need him for a few weeks so why not ride this strikeout train? I'll acknowledge his MLB track record isn't the best, but the potential for a star is there and he's just a click away on the waiver wire.

Replacing the star pitcher in the long term (Ex. Derek Holland, Jeremy Hellickson)

Some players are out a little longer, and in these cases you want to replace them with arms that are slated to give you innings, rather than lottery tickets. Rotation security is paramount here, since you'll need a half season or potentially more to fill these cats' shoes.

Martin Perez, SP Texas Rangers (Ownership: 28.7 percent)

Perez has a bit of a spotty track record in the minors, but he's entrenched right now in the Rangers rotation, with a five-pitch arsenal, and a 10-6 season with a sub-4.00 ERA under his belt. His strikeout numbers in 2013 were just okay, but he put up impressive numbers in a hitter haven. He can be a reliable source of stats at the back end of your fantasy rotation.

Rick Porcello, SP Detroit Tigers (Ownership: 39.6 percent)

If you're searching for strikeouts, you're in the wrong place. Porcello is a ground ball pitcher through and through, but as he's matured his profile is trending upward despite what the ERA says. Over the last two year's he's been victimized by the home run excessively, despite not even surrendering that many fly balls, but it's unlikely to continue as Comerica park tends to favor pitching.

Playing for the Tigers likely means he'll get a ton of wins as well. Even though he's had ERAs of over 4.00 the past two seasons, he's still been able to reach 13 victories both times. With some regression to the mean, expect Porcello to become a 15-game winner or better.