David Robertson now Yankees' best reliever

The greatest closer in the history of baseball has likely been lost for the season, if not his career.

Mariano Rivera -- owner of an all-time record 608 saves, eight 40-save seasons and a record 15 consecutive seasons of 25 or more saves -- suffered a nasty-looking knee injury Thursday while shagging fly balls during batting practice at Kansas City's Kauffman Stadium. He was in obvious pain, required assistance getting up and was carted off the field. Though the New York Yankees officially announced the injury a "twisted knee," Rivera had an MRI exam Thursday evening and manager Joe Girardi announced that the preliminary report on Rivera indicates a torn ACL, an injury that typically requires season-ending surgery. It should be noted that we do not yet have the official word on the injury or the prognosis for recovery, but Rivera's owners are understandably disappointed -- a sentiment shared by those who have already lost Brian Wilson, Ryan Madson and Joakim Soria for the season. In fantasy, the waiver wire waits for no one. Who might now replace Rivera in the ninth inning?

Though a specific replacement wasn't immediately named, the smart move is to immediately dash to the waiver wire to grab David Robertson (available in 85 percent of leagues prior to the injury). He has been the Yankees' primary eighth-inning reliever thanks to a remarkable run since the beginning of last season, posting a 0.93 ERA, 1.09 WHIP and 13.67 strikeouts per nine innings in 81 appearances during that span.

Besides deepening his arsenal -- the addition of a cutter has been a plus -- greater pitch efficiency has been crucial for Robertson to break out to this extent. After averaging 19.09 pitches per inning in 2010, he cut that number to 18.20 last season and 18.00 in 2012. He has also been a beast in difficult situations, recording a 1-for-20, 14-K performance with the bases loaded since the beginning of 2011, while holding batters to a .180 AVG/.291 OBP/.240 SLG line in late-and-close situations and a .186/.292/.236 in high-leverage outings. So Robertson, at least statistically speaking, looks more than capable of filling in, even beyond this season.

Frankly, on skills alone, Robertson could by all rights be the No. 1 closer in fantasy for the remainder of the season, if he is granted the opportunity. It sure helps that he pitches for the Yankees, a team that wins a lot, and therefore is as likely to generate a healthy number of save chances as anyone.

If you're wondering about Rafael Soriano, the ex-Tampa Bay Rays closer, it's not unthinkable that he could instead sneak into the role. When he signed a three-year, $35-million deal with the Yankees, he was seen as Rivera's eventual successor. Soriano has more "closer experience" than Robertson, if such things matter to manager Joe Girardi.

But Soriano has been clearly outpitched by Robertson during his Yankees career; his 3.80 ERA, 1.42 WHIP and 8.37 K's-per-nine ratio pale in comparison to Robertson's numbers cited above. Soriano also missed two months with an elbow injury last season, an absence that allowed Robertson to leapfrog him on the depth chart. Soriano might also not have quite the impact in fantasy as Robertson could, since his numbers haven't been as stellar. Expect some rocky outings if he's picked.

The Yankees should promote everyone accordingly while Rivera heals. Robertson should close with Soriano setting him up -- or vice versa -- while pitchers like Cory Wade and Boone Logan take on more important roles, mostly affecting those in holds leagues.

But, before concluding, let's not forget Rivera's substantial contributions to fantasy baseball, if this indeed signals the end of his storied career. Simply put, the game is better when a Hall of Fame talent like him is healthy and productive. He'll be missed, not only by his fantasy owners, but by all baseball fans.