The first game of a three game set begins with Aaron Harang on the mound against Jon Niese. The Braves are going with a right-handed heavy lineup against the southpaw. For Niese's career, he has allowed righties to hit .270/.332/.414 against him, so sitting Jason Heyward in favor of Ryan Doumit is understandable if he was planning on finding a day to get him off anyway.
The defense without Heyward and with Doumit obviously takes a big hit, and Harang has been a high percentage fly ball pitcher so far, so hopefully that decision does not come back to bite them.
The Mets have not yet released their lineup, most likely due to a trade they are currently making. When they fill out their lineup card I will update the post.