Kemp singled in the winning run in the bottom of the 10th inning after homering in consecutive games for the first time in over a year and the Dodgers beat the Atlanta Braves 3-2 Wednesday night for their season-best fifth straight victory.
"Boy, is he locked in right now," Atlanta starter Alex Wood said.
Los Angeles leads San Francisco by three games.
Zack Greinke struck out a season-high 13 and departed with the lead, but didn't factor in the decision. He is 14-3 at Dodger Stadium with a 2.27 ERA in 23 home starts with the team.
"All the pitches were working," he said. "A lot of stuff came together."
Kemp scored the Dodgers' first two runs of the game, including his 11th homer leading off the second.
"He's been swinging the bat pretty well now," Greinke said of Kemp. "The biggest difference is the power that comes with it. The past week the ball's been driven. It's pretty exciting to see."
Kemp notched his ninth career walk-off hit, and first since July 18, 2012, against Philadelphia. He hadn't homered in consecutive games since last July.
"It's a great feeling knowing you helped the team win a game," he said. "We're pretty confident every day. It feels good to be in position to score a run or take that extra base. I'm not as fast as I want to be, but it's coming."
J.P. Howell (3-3) got the win in relief, walking two and striking out one in one inning.
"As soon as it left my hand I just prayed for Justin not to hit it," Jansen said.
Upton's brother, B.J., struck out four times.
Greinke allowed one run and five hits in eight innings while walking one. He was making his first start at home since June 28.
Kemp, who homered twice on Tuesday night, tied the game 1-1 on his 11th homer of the season.
Simmons had an RBI single that gave Atlanta a 1-0 lead in the second.
Wood gave up one run and six hits in seven innings. He struck out eight and walked two.
"Greinke's pretty impressive," Wood said. "I was happy I was able to go toe-to-toe with him for seven innings."
Braves: Outfielder Jason Heyward was out of the lineup for the second straight day with a sore back he strained last week chasing a foul ball. Jordan Schafer started in right field for the first time this season. Manager Fredi Gonzalez said it's likely he'll give Heyward an extra day off once he says he's ready to go again.
Dodgers: Greinke said his calf was sore in the first couple of innings but got better as the game went on. Hyun-Jin Ryu will get an extra day of rest before he starts on Saturday. Dan Haren, who has lost all four of his starts this month, will take the mound for Friday's series opener against the Cubs.
Braves: Julio Teheran (10-6, 2.71 ERA) takes the mound for the series finale on Thursday. The only time the right-hander has faced the Dodgers was in last year's NL division series, when he tossed 2 2/3 innings in a loss.
Dodgers: Clayton Kershaw (12-2, 1.76 ERA) is coming off a three-hit shutout victory over the Giants in his last start. The left-hander leads the NL with 11.30 strikeouts per nine innings as a starter. He has 140 strikeouts and 15 walks in 112 1/3 innings.
Gonzalez was 1-1 on challenges. He lost on a pickoff play with the go-ahead run on base in the 10th. Schafer walked and was sacrificed to second by Ramiro Pena. Howell turned and fired, with Dee Gordon completing the pickoff to empty the bases. Gordon was involved in the Braves' first challenge in the third. He attempted to steal second and was called safe, but was ruled out when the call was overturned.