I frankly would never have brought Kimbrel into that particular 8th inning--not in the very first game of the season. Horrible precedent because it basically says, "only my closer for the 8th and 9th innings, even when we have a 4 (or even a 2 run) lead."
We have the benefit of hindsight. But even then my memory is that Kelly had at least two 8 pitch counts on walks which came on 3-2 counts. So close. Also, we should not forget that, while Smith walked the first guy to make the score 4-2, he struck out the second guy for the 2d out of the inning. The bases were still loaded, but we only needed one out. Me, I almost certainly stay with Smith, and I sure as heck don't bring in a newbie. Later in the season, sure, bring in Kimbrel for the last out.