It took two months, but it finally happened on Sunday afternoon: Both teams challenged one play.
Let's set the scene: The Rangers had runners on the corners with two outs against the Nationals. Alex Rios attempted to steal second base, and when catcher Wilson Ramos threw down to second, Elvis Andrus broke for home from third base. Rios initially slid in safe, but he came off the bag just a tiny bit and was tagged out. Andrus scored before the out was made and the inning ended.
Nats manager Matt Williams wasn't sure about that, however. He challenged that Andrus did not cross the plate before Rios was called out, which meant the run should not have counted. The umpires reviewed it, and, sure enough, Williams was right. The call was overturned and the run was taken off the board. That's when Rangers manager Ron Washington came out of the dugout to challenge whether Rios was actually tagged out in the first place. To the video:
As you can see, Rios was clearly tagged out before Andrus crossed the plate, so the umpires got it half-right. The out was made but the run should not have scored. Williams won his challenge, Washington lost his. Texas went on to win the game 2-0.
This is a new MLB, folks. More calls are correct than ever before and it's pretty awesome.