"Every win up to this point is going to be big," Kemp said as the Dodgers trimmed their magic number for clinching their third postseason berth in four years to nine.
Los Angeles began the day with a five-game lead over Colorado in the NL West -- its largest since being 5½ games up on the Rockies on Sept. 1.
The Dodgers' first three-game winning streak since Aug. 20-22 against the Chicago Cubs left them 29 games above .500 for the first time since the penultimate day of the 1985 season.
Kemp sent an 0-2 pitch from Kevin Hart (1-6) into the right-field pavilion for his 24th homer, driving in Belliard and giving the Dodgers a 2-1 lead en route to their 38th comeback win of the season. Kemp extended his career highs for homers and RBIs (94) with his first longball since Sept. 1.
"I didn't think I would be here this quick doing all these good things," he said. "I'm letting the game come to me."
Kemp's shot came about 15 hours after Ethier's two-run homer in the 13th inning lifted Los Angeles to a 5-4 victory.
"It was a real important game for us to win, coming back from the game last night and knowing you have a psychological advantage," Dodgers manager Joe Torre said. "We were able to hold up."
Belliard made it 3-1 in the eighth, hitting the first pitch from Phil Dumatrait over the wall in center. Dumatrait gave up Ethier's winning homer on the first pitch a night earlier.
Belliard is hitting .319 with three homers and eight RBIs in 13 games since being acquired from Washington on Aug. 30.
"It's been fun since I got here, they give me a hug every day," he said.
Hiroki Kuroda (7-6) gave up one run and six hits, struck out seven and walked none in his third start since returning from the disabled list after being hit on the right side of his head by a comebacker at Arizona on Aug. 15.
"A little bit of a surprise that he was able to really get back to normal that quickly because he had to deal with a great deal of trauma, not to mention the concussion," Torre said. "To have him jump in there this time of year is important because of what he did last year for us."
Jonathan Broxton pitched a perfect ninth for his 35th save in 40 chances.
Hart allowed two runs and seven hits in six innings, losing his fifth consecutive start.
"I'd like to have one of those pitches back. It was supposed to be a sinker in, but I kind of just pushed it and it was up in the zone and right in the swing path," he said. "It was the exact opposite of what I wanted to do."
Jason Jaramillo had an RBI single in the second for Pittsburgh, which has lost 17 of 19.
"I can't ever say I'm happy about losing three games in a row, but you can't say enough about how the guys battled," manager John Russell said. "We fell short in all three games, but you can't fault the effort. We get into games like this, and unfortunately it comes down to one pitch or one play, and very good teams take advantage of that."
The crowd of 53,193 was the Dodgers' seventh sellout and the largest weekday attendance in stadium history, excluding opening day. The main attraction was another Manny Ramirez bobblehead giveaway. ... Dodgers RHP Chad Billingsley, who has lost four of his last five starts, won't take his scheduled turn in the rotation this weekend against the Giants, replaced by RHP Vicente Padilla. RHP Jon Garland will pitch Saturday, followed by LHP Randy Wolf on Sunday. Torre said he told Billingsley that "we needed to get him straightened out." ... Crew chief Gerry Davis missed the start of the game because of illness, but took his spot in the middle of the third.