The Red Sox entered Sunday’s doubleheader riding a seven-game winning streak. Roughly nine hours later, they find themselves trying to avoid a three-game losing streak. Over the course of a 162-game slate, a team is bound to go through ups and downs, so the important thing is to remain on an even keel. That doesn’t mean Sunday’s pair of losses won’t still sting, though, especially given how the day started for Boston. The Sox were riding high entering Sunday’s action. Daniel Nava’s eighth-inning home run on Saturday capped off an emotional day at the ballpark, and the Red Sox looked as if nothing could stop them. Over the course of Sunday’s games, though, the Red Sox failed to capitalize on some opportunities, and they thus let two winnable contests slip through their fingertips. In Game 1, Ryan Dempster essentially had one rough inning that proved costly. The Royals put up three runs in the fourth to grab a 4-2 lead, and Kansas City cruised from there. The Sox had a chance to stage a rally in the eighth inning, but they left the bases loaded when Jarrod Saltalamacchia grounded lazily back to the mound. The Royals struck first in Game 2, as they did in Game 1, but the Red Sox again found themselves with a lead. Again, however, they let that lead slip away. This time, it was the bullpen that was responsible for giving the Royals life, as the usually reliable Koji Uehara gave up a game-tying home run to Billy Butler in the eighth inning and Andrew Miller’s control issues gave Kansas City the advantage in the 10th.