It took two days, but it was only a matter of time before MLB's new replay review system exposed its single biggest flaw. And it happened in a big way, on a play that very directly affected the outcome of a game.
With two outs in the fourth inning, the Giants attempted to pick A.J. Pollock off of first. Shawon Dunston is the Giants' replay pointman, and from his station inside the clubhouse, he alerted manager Bruce Bochy by phone that he should challenge the call. Bochy did, but was unsuccessful—Pollock was still safe. (Despite cameras catching Pollock mouthing "they got me" after he saw a replay on the jumbotron.)
Pollock would move to third on a double, then come home on a passed ball. The play at the plate was close, but replays clearly showed that Pollock should have been out, tagged on the heel by Matt Cain.
Because the Giants had used, and lost, their challenge, they were unable to ask the umpires to review this one. This was an inevitability because of the replay review system's two provisos: that a manger gets one failed challenge, and that umpires can not initiate a review on their own until the seventh inning.
These are artificial limitations, and are bound to create windows for blown calls just like the one we saw last night. It needn't be this way. The challenge system exists as a sop to those worried about slowing the game down, but Bruce Bochy's argument on the play at the plate took just as much time as a review would have. If review exists to get the call right as often as possible—and the Diamondbacks would go on to win this game by a single run—do away with challenges altogether and let the umpires decide when to go to replay.