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Cole Hamels of the Philadelphia Phillies.
Cole Hamels and Jon Lester, both 29, aren't far off the Hall of Fame track. The former has been a World Series MVP, while Lester threw a no-hitter in 2008 and has since spent several seasons as a rotation leader. However, their major league service time pales in comparison to most members on this list, and neither is even the best pitcher on his own team so far in 2013.
Madison Bumgarner, Aroldis Chapman and Chris Sale are all coming off terrific years. They're all 25 years or younger, so it's far too soon to include them on these sort of lists. Their sample sizes are too small.
Though John Franco has the most saves of any left-hander in MLB history, he enjoyed few "dominant" campaigns. His improved strikeout rate with the New York Mets is misleading. From 1991 through his retirement in 2005, Franco had light workloads. He only pitched more than 60 innings once in that span.
Journeyman David Wells maintained an impeccable walk rate and totaled nearly 3,500 innings in his career. He completed a perfect game and excelled in October. But one season above 5.0 WAR and distant third-place finishes in 1998 and 2000 AL Cy Young Award voting doesn't cut it.
Vida Blue and Ron Guidry actually won Cy Youngs in 1971 and 1978, respectively. Unfortunately, neither guy had a particularly long career. Because Frank Tanana thrived during his time with the California Angels and continued working through his 40th birthday, he would have been No. 21 on an expanded list of left-handers.
And going back even farther, there was Babe Ruth. We often remember his offensive dominance with the New York Yankees while overlooking his combined 15.2 WAR as a pitcher on the 1916-1917 Boston Red Sox. He also led the Sox to the 1918 championship (2-0, 1.06 ERA, 1 SHO in World Series).