"We have to figure out some things so guys can get some outs later in the game," Diamondbacks manager Kirk Gibson said.
Leading 5-3, Arizona had its lead trimmed when Adrian Gonzalez hit a leadoff homer in the seventh inning. Bell got two quick outs in the ninth, but walked Gonzalez.
Pinch runner Jerry Hairston Jr. moved to second on Hanley Ramirez's single, then scored on A.J. Elllis' run-scoring single to tie the game.
Bell's fifth blown save and the 19th by the Diamondbacks gave the Dodgers life, and they finished off the Arizona in the 14th, when Ramirez and Ellis hit consecutive homers off Collmenter (4-2).
"I feel really bad because I left everybody down," said Bell, who's allowed nine runs his past 11 outings. "We definitely should have won that game."
Kenley Jansen (3-3) pitched the final two innings for the Dodgers, who used all of their position players and had Zack Greinke, Monday's starter, pinch hit in the 10th inning.
A team that was 12 games under .500 and 9½ games out of first on June 22, the Dodgers are back to .500 and 1½ games back of the Diamondbacks in the NL West after winning 15 of 18.
"Obviously, you want to come in and win a series, but to win three was big for us because it's a two-game swing when you're playing them," Dodgers manager Don Mattingly said. "I really felt like before we got here, we really got ourselves back into it, where we were in the race and we knew it. This has been icing on the cake."
Tyler Skaggs had a superb return to Arizona's rotation on Friday, allowing three hits and striking out five in eight scoreless innings against Colorado after being called up from Triple-A Reno. The left-hander wasn't nearly as good against the Dodgers, giving up a run on Scott Van Slyke's sacrifice fly in the fourth inning and a two-run double to Ramirez that put the Dodgers up 3-2 in the fifth. Skaggs then walked two to load the bases, but reliever Will Harris prevented further damage by getting Van Slyke to hit into an inning-ending double play.
Skaggs allowed three runs on eight hits in 4 1-3 innings.
Arizona went through eight pitchers in the 19th game in the majors to go at least 14 innings this season, according to STATS. There were 20 total last season.
Aaron Hill homered and drove in two runs, and Paul Goldschmidt hit a two-run double for the Diamondbacks, who went seven innings until two outs in the 12th without a hit.
Even after Bell's blowup, the Diamondbacks had chances, as did the Dodgers.
But, with fans falling asleep in the stands, Ramirez and Ellis finally put the Dodgers ahead for good, sending the Diamondbacks to their third consecutive loss.
"We have to be much better to continue to stay in the race then we have been in the first half," Gibson said. "We try to put guys in situations and it hasn't worked. We will certainly look at different options."