Kemp was credited with crossing home to give Los Angeles a 6-0 lead in the fourth, even though TV replays showed the inning's last out already had been recorded on third baseman Ryan Zimmerman's head-over-heels, reaching tag of runner Adrian Gonzalez.
That extra run loomed large when the hosts — who had won the opener 3-1 thanks largely to Jordan Zimmermann's six innings of one-run baseball — wound up sending 12 batters to the plate while scoring six runs in the eighth.
Michael Morse had a homer and a two-run single, and Washington chased Josh Beckett, who had allowed only two hits through seven innings.
The announced crowd of 26,931 was getting loud, perhaps anticipating a comeback and playoff-clinching victory, when Kemp drove an 0-2 pitch from Tyler Clippard (2-5) over the wall in centre for his 19th homer.
Ronald Belisario (7-1) earned the win by getting the last two outs of the eighth inning. Brandon League picked up his third save with a hitless ninth.
Zimmermann (11-8) allowed one run and six hits in six innings in the opener. Clippard pitched the ninth for his 32nd save.
Dodgers starter Aaron Harang (9-10) lasted just 4 2-3 innings in the first game.
BRAVES 3, MARLINS 0
MIAMI (AP) — Kris Medlen pitched eight innings of four-hit ball and the Braves won his start for the 21st straight time.
Medlen (9-1) lost the first two starts of his career in 2009. He hasn't taken a loss in any of his 26 starts since, with the Braves prevailing in the last 21 of those — making them the first team since the New York Yankees to have such a streak, according to STATS LLC.
The Yankees won 22 straight times when Whitey Ford started games from 1950 through 1953, a span interrupted by Ford serving in the Korean War.
Chipper Jones, playing his last game against Miami, went 1 for 4, getting hit No. 2,721 to tie Gehrig for 58th on baseball's career list.
Rob Brantly doubled for Miami, which was shut out for the 16th time this season. Josh Johnson (8-13) gave up three runs in six innings.
Craig Kimbrel picked up his 38th save in 41 chances for Atlanta.
PHILLIES 3, METS 2
NEW YORK (AP) — Ryan Howard hit a go-ahead homer with two outs in the ninth inning and the Phillies rallied for a dramatic victory.
Jimmy Rollins hit a leadoff home run but the Phillies went into the ninth with only two hits. Chase Utley worked a two-out walk against rookie Josh Edgin (1-2), filling in for ailing Mets closer Frank Francisco, and Howard launched a 93 mph fastball off the facing of the second deck in right field to give his team a 3-2 lead.
Trying for a last-gasp post-season charge after a miserable first half, the surging Phillies (75-74) won for the 10th time in 13 games. They remained four games behind St. Louis for the second NL wild-card spot.
Jeremy Horst (2-0) got the win and Jonathan Papelbon worked a one-hit ninth for his 36th save in 40 tries.
David Wright hit a solo homer but the Mets (66-82) dropped their eighth straight home game and 24th in the last 28 at Citi Field.
BREWERS 3, PIRATES 1
PITTSBURGH (AP) — Marco Estrada pitched seven scoreless innings and rookie shortstop Jean Segura hit a double and triple as the surging Brewers stayed in contention for a post-season berth.
Estrada (4-6) allowed three hits and retired his last 10 batters while improving to 4-1 with a 1.23 ERA in his last six starts. John Axford of Simcoe, Ont., worked around Andrew McCutchen's leadoff home run in the ninth inning while recording his 30th save in 38 opportunities.
Milwaukee has won four straight games, seven of eight and 22 of 28. They remained 2 1/2 games behind St. Louis in the race for the second NL wild card.
Pittsburgh has lost 14 of 18 and 20 of 27 to drop to 74-74, the first time it has been at .500 since it was 26-26 on June 2. Rookie Kyle McPherson (0-1) took the loss in his first major league start, giving up two runs and seven hits in 4 1-3 innings.
CARDINALS 5, ASTROS 0
ST. LOUIS (AP) — David Freese and Yadier Molina each hit their 20th home run of the season, and Lance Lynn threw 6 1-3 innings to lift the Cardinals to the win.
St. Louis now leads the Los Angeles Dodgers by two games in the race for the second wild-card spot in the National League. Milwaukee is 2 1/2 games back.
The Cardinals have won seven straight against lowly Houston. They have won three in a row overall for the first time since a four-game streak from Aug. 21-24.
Lynn (16-7), in his second start following a demotion to the bullpen, allowed three hits in a 102-pitch stint.
Freese hit a two-run homer off Lucas Harrell (10-10) in the second inning. Molina added a solo shot in the fourth.
REDS 6, CUBS 5, 11 INNINGS
CHICAGO (AP) — Drew Stubbs hit a tie-breaking RBI single in the 11th inning and Cincinnati beat Chicago hours after Reds manager Dusty Baker left the ballpark for chest X-rays.
A team spokesman said the tests were to "rule out pneumonia." Bench coach Chris Speier brought the lineup card to home plate and there was no sign of the 63-year-old Baker during the game.
Brandon Phillips' lazy popup with two out in the 11th was misplayed by Cubs right-fielder David DeJesus, allowing him to reach second. Stubbs then smoked a run-scoring single to left against Alberto Cabrera (0-1).
Logan Ondrusek (5-2) worked out of a bases-loaded jam in the 10th to earn the win. Jonathan Broxton earned his fourth save in six chances since joining Cincinnati in July.
DIAMONDBACKS 6, PADRES 2
PHOENIX (AP) — Adam Eaton tripled to spark a three-run fifth inning and Arizona rallied to beat San Diego.
Dan Wheeler had an RBI triple, and Miguel Montero and Paul Goldschmidt added run-scoring doubles for the Diamondbacks, who have won three straight. Arizona remained 4 1/2 games behind St. Louis for the second NL wild card.
Arizona starter Trevor Cahill (12-11) went six innings, allowing two runs and five hits with four walks and four strikeouts.
Max Venable and John Baker had consecutive RBI singles for the Padres, who have lost two straight to the Diamondbacks after winning eight of their previous nine against them.
Padres starter Edinson Volquez (10-11) gave up four runs and eight hits over six innings.
GIANTS 7, ROCKIES 1
SAN FRANCISCO (AP) — Matt Cain pitched eight solid innings to earn his career-best 15th win, Pablo Sandoval homered for his first time in two months and San Francisco moved another game closer to clinching the NL West title.
Sandoval's three-run shot in the first inning off Tyler Chatwood (4-5) was his ninth homer of the season and helped hand Cain (15-5) another milestone in a season full of them. With the second-place Dodgers splitting a doubleheader in Washington, San Francisco (86-63) lowered its magic number to clinch the division to five.
Cain allowed four hits, struck out eight and walked four. Chris Nelson scored Colorado's only run on D.J. LeMahieu's flyout in the fifth.