After Uggla led off with a walk, Simmons hit the ball too deep into the gap in left-center field for Carlos Gonzalez and Dexter Fowler to keep it from reaching the wall.
Scott Downs (1-0) earned the win after being acquired in a trade with the Los Angeles Angels earlier in the day and arriving at Turner Field not long before the first pitch. The left-hander allowed one hit and struck out one in 1 1/3 innings.
Escalona (1-4) allowed one hit, one run and one walk in 12 pitches.
Downs escaped a bases-loaded jam in the ninth by making just one pitch, a liner he caught on the mound from Todd Helton.
Gonzalez went 5-for-5 with two RBIs after missing the last three games with a sprained middle right finger. He drove in the tying run in the ninth off Jordan Walden.
Atlanta’s offense bailed out starting pitcher Brandon Beachy, who made his first start in 13 months after undergoing elbow ligament replacement surgery.
Chris Johnson, who leads the NL with a .339 batting average, and Uggla each had two RBIs to help the Braves erase a 5-0 hole with six runs in the third inning, then rally from a two-run deficit in the fifth to make it 8-7.
Beachy gave up eight hits, seven runs and one walk with five strikeouts in 3 2-3 innings. He made 84 pitches, 58 for strikes.
With Braves closer Craig Kimbrel unavailable after earning saves in all three games against St. Louis last weekend, Walden gave up two hits, walked two in two-thirds of an inning and left with the bases loaded.
Rockies starter Jorge De La Rosa gave up 10 hits and eight runs — five earned — with two walks and three strikeouts in five innings.
The Braves scored six runs in the bottom of the third to take a 6-5 lead, due in part to a fielding error by third baseman Nolan Arenado that ruined a chance for an inning-ending double play.
After Jason Heyward’s one-out RBI single made it 5-1, Arenado let Evan Gattis’ bases-loaded grounder bounce off the heel of his glove, allowing Heyward to score and keep the bases loaded.
Johnson followed with a two-run double before Uggla had an RBI groundout and Simmons’ RBI double gave the Braves a 6-5 lead.
The Rockies scored twice in the fourth to go ahead 7-6 when Arenado hit his eighth homer. D.J. LeMahieu’s single chased Beachy and Gonzalez scored on David Carpenter’s wild pitch.
Manuel Corpas pitched the sixth and seventh, Josh Outman and Wilton Lopez combined to pitch the eighth and Matt Belisle pitched the ninth for Colorado.
Luis Ayala allowed one hit in the seventh and Luis Ayala two hits in the eighth for Atlanta.
All of Gonzalez’s five hits were singles, raising his average nine points to .306. Gonzalez matched his career high for hits, which he last accomplished in a 9-4 victory at the Chicago Cubs on May 14.
The Rockies took a 1-0 lead in the first on Gonzalez’s RBI single and went up 2-0 in the second on Wilin Rosario’s 15th homer.
In the third, Colorado led 4-0 on a two-run triple by Michael Cuddyer, who scored to make it 5-0 on Helton’s sacrifice fly.
Beachy last pitched on June 16, 2012, against Baltimore. He missed 105 games recovering from a torn right elbow ligament and was tied for the major league lead with a 2.00 ERA when he was injured.
Notes: Walden blew his second straight save opportunity and first since April 26, 2012, when he pitched for the Los Angeles Angels at Tampa Bay. ... Atlanta improved to 8-4 in extra innings. Colorado dropped to 5-8. ... De La Rosa had gone 3-1 with a 1.96 ERA in his last seven starts. He left for a pinch-hitter in the sixth.