Rendon scored twice and drove in a pair as the Nationals salvaged a split of the four-game series with the Braves to enter the All-Star break with a 9 1/2-game lead over Atlanta in the National League East.
Washington starter Joe Ross left the game with an apparent injury with one out in the fourth.
Reliever Matt Grace (1-0) allowed two runs, one earned, over 2 2/3 innings. Joe Blanton, Enny Romero and Matt Albers each threw a scoreless inning.
With Washington leading by one, Rendon provided an insurance run in the seventh. He walked, stole second and went to third on a throwing error by catcher Tyler Flowers. Rendon scored on a Matt Wieters’ sacrifice fly.
The Nationals pulled away with three runs in the eighth.
Atlanta’s Johan Camargo had three hits, including a solo home run — his first in the majors — and a walk. Freddie Freeman added a three-run homer and a single.
Chris Heisey’s RBI-double broke a 3-3 tie in the fourth and Wieters smacked a two-run single in the fifth.
Camargo’s homer and a Nick Markakis fielder’s choice pulled Atlanta within 6-5 in the sixth. The second run was unearned following a two-base error on Bryce Harper that allowed Freeman to go all the way to third on a single.
After Ross got Markakis to start the fourth, pitching coach Mike Maddux came out to the mound and was soon joined by the team trainer. Manager Dusty Baker then came out and Ross was removed in favor of Grace.
Ross, whose velocity appeared lower than his norm, allowed three runs on three hits over 3 1/3 innings.
Washington led 3-0 when Ross issued a pair of two-out walks in the third and Freeman followed with his 16th homer of the season.
Atlanta rookie Sean Newcomb (1-4) allowed four runs on four hits over four innings.
Rendon’s two-run double capped a three-run Washington first as Newcomb threw 39 pitches.
Following the All-Star break, the Braves open a three-game series against the Diamondbacks on Friday in Atlanta.