Based on fangraphs numbers, since 2002, Mo has 386 saves and has blown 38 of them (so he converted ~90% of all opportunities). Blown saves were not recorded before 2002.
According to google, between the regular season and postseason, Mariano Rivera has had 74 save opportunities against the Red Sox. He has blown 16 of them. (converting only ~78% of all opportunities).
Not to say that Mo Rivera isn't awesome and that I don't prepare to turn off the TV when he comes in against us, but singling out with "bane of boston" seems silly.
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