Both faltered in the ninth inning on Tuesday, when the Washington Nationals overcame a two-run deficit to beat the Atlanta Braves 6-5 in the makeup of a series opener postponed by a shooting rampage a day earlier at the nearby Navy Yard.
Simmons allowed Denard Span's grounder off Kimbrel to bounce through his legs as two runs scored on the game-ending error.
"The numbers were probably pretty well stacked against us," Washington's Ian Desmond said. "But they have been for a while now, so we're just going out and playing."
Pinch-hitter Chad Tracy had an RBI grounder against Kimbrel as Washington kept Atlanta's magic number at four for clinching the NL East for the first time since the Braves' streak of 11 consecutive division titles from 1995-05. A sweep of the day-night doubleheader would have sealed the division for Atlanta.
Washington closed within 4½ games of Cincinnati for the NL's second wild-card berth with 12 games remaining.
"By no means are we to, I guess, the pot of gold at the end of the rainbow yet," Desmond said." But we are playing better, and I think that's all that anybody in here really wanted to see."
Kimbrel (3-3), who leads the major leagues with 47 saves, blew a save chance for just the fourth time this season.
Atlanta trailed 3-0 but took a 4-3 lead in the eighth on Evan Gattis' two-run homer off Tyler Clippard on an 0-2 pitch, which stopped an 0-for-18 skid. The Braves added a run in the ninth when Elliot Johnson singled, advanced on a throwing error by left fielder Bryce Harper, stole third and came around as Desmond allowed Freddie Freeman's four-hop grounder to shortstop to bounce off the heel of his glove for his 18th error this season.
"It's only fitting the way it turned out that we got their Superman closer," Nationals manager Davey Johnson said. "That was worth it all."
In the ninth, Adam LaRoche walked on a full count, Wilson Ramos reached on an infield single and Anthony Rendon walked on a 3-2 pitch. After Tracy's grounder, Atlanta elected to pitch to Span with first base open, and he hit a three-hopper over the mound that rolled past Simmons into center field. Span was given an RBI, with the second run scoring on the error.
"If you don't get your job done, you want to go out there as fast as you can and do it again," Kimbrel said. "Hopefully, we score some runs and are winning in the ninth inning in this next game, and I can go in and shut it down."
Ian Krol (2-1) faced two batters in the ninth, giving Washington its first win in seven home games against Atlanta this year and sparing Clippard the loss.
"He felt terrible," Nationals starter Dan Haren said of Clippard. "He was yelling for 15 minutes straight, screaming in the locker room. How many times has the guy picked us up this year in huge games? Has so many holds. The guy pitches six out of seven days. The guy has been money all year. It's nice for us to pick him for once, and I know after the game he was going crazy, too. So, he felt great about it. It just shows you it's the time of year where you just kind of throw personal stuff out the window. It's just about winning the game."
Before the game, both teams stood in front of their dugouts, heads bowed, and a color guard was stationed behind home plate during a minute of silence to pay tribute to the people killed Monday and those affected by the shootings.
Span's second-inning single extended his hitting streak to 27 games, matching Colorado's Michael Cuddyer for the longest in the major leagues this season.
Freeman's sixth-inning sacrifice fly off Haren made him the first Atlanta player with 100 RBIs in a season since Chipper Jones and Jeff Francoeur in 2007, and pinch-hitter Dan Uggla singled in a run in the seventh.
Minor retired his final 13 batters. ... RHP Stephen Strasburg's bullpen session Monday went "great," Nationals manager Davey Johnson said. Strasburg is set to start Thursday against Miami after missing Friday's turn due forearm tightness in his pitching arm. ... Adm. James Winnefeld , the vice chairman of the Joint Chiefs of Staff, greeted players in the Nationals clubhouse before the game, handing out blue and gold Navy caps to wear during warmups.