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This one promises to be extremely interesting, since Arrieta has been virtualy an unstoppable force over the past few months - he is 16-1 in his last 20 starts, with an 0.86 ERA. Let me repeat that: oh point eight six. Has there ever been such a dominant streak of 20 starts? Checking Bob Gibson's 1968 season, I did find a 20-game spell [starts 11-30], where he had an 0.79 ERA. But the run environment of that time was almost a full run lower than 2015, with the NL ERA that year below three, for the only time in the live-ball era. He has faced the Pirates five times this year, and had a 0.75 ERA, having allowed three runs over 36 innings. However, they did beat him on May 17,
The presence of Arrieta may tilt the balance of favor in this contest towards the Cubs, despite the fact that they finished the regular season with a worse record, which is why the game is being played in Pittsburgh. It's kinda ironic that the Cubs' 97 wins would have been good enough to take any other division in baseball - winning the AL West by nine games! - but was "only" good enough for third place in the NL Central. They took the second NL wild-card spot by thirteen games from the Giants. It's kind of a poison pill that the Cardinals will have to face the winner, rather than, say the Mets, whose regular season record was seven or eight games worse than the Cubs and Pirates respectively.
It will, however, be a benefit that St. Louis will not have to face Arrieta or Hamels twice in a short series - most likely, only in Game Three of the NLDS. That's significant, since the Cubs are 25-8 when Arrieta starts this year, compared to 72-57 when he doesn't, and the dropoff to Jon Lester and Kyle Hendricks is palpable. The same goes for the Pirates, with Cole clearly better than A.J. Burnett and Francisco Liriano, though the gap there isn't perhaps quite as much. However, they're still 23-9 when he starts, compared to 75-55 when he doesn't, so it's clear that the new wild-card format is definitely doing what it's supposed to, and providing an edge to division winners.