Sierra, who is ranked the Cardinals' No. 4 prospect, jump-started a fifth-inning rally with a bunt single off reliever Chris Ellis. Jacob Wilson tied the game with an RBI single and then scored on a wild pitch. Matt Adams' sacrifice fly capped the scoring for St. Louis.
The 19-year-old Sierra, who came over from Minor League camp for the day, added a stolen base, outfield assist and run scored to his two-hit day.
"I just threw him in there to see what happens," Cardinals manager Mike Matheny said. "He just looks like he can do a little bit of everything. He's fun to watch."
The Braves had taken a second-inning lead on Blake Lalli's two-out RBI single off Cardinals starter Carlos Martinez, who pitched two innings in his Grapefruit League debut. The outing was Martinez's first since a right shoulder injury prematurely ended his season last September. He hit 99 mph on the radar gun, struck out two and threw 19 of his 26 pitches for strikes.
Braves starter Jhoulys Chacin went even deeper, finishing three scoreless innings in what was his second start of the spring. Chacin scattered three hits while striking out two and walking one. He threw 34 pitches, 23 for strikes.
"I feel really healthy, finally, and everything is just going well," said Chacin, who is in Braves camp on a Minor League contract. "I want to keep doing what I've been doing, and pitch the way I know I can."
Reliever Seung Hwan Oh made his third scoreless Grapefruit League appearance for the Cardinals. Deck McGuire and Jeremy Hefner followed with scoreless two-inning outings.
Atlanta's Ryan Weber also pitched a pair of scoreless frames. Braves outfield prospect Hector Olivera tallied his fourth multihit game of the spring.
Up next for the Braves:Manny Banuelos will make his first Grapefruit League when Atlanta hosts the Nationals on Saturday at 6:05 p.m. ET. As long as he remains healthy, Banuelos appears to be the favorite to begin the season as Atlanta's fifth starter. This will be the Braves' first night game of the year, and fans can catch the action on Gameday Audio.
Up next for the Cardinals: The Cardinals will play a pair of split-squad games on Saturday, with manager Mike Matheny bringing part of the club to Port St. Lucie to face the Mets while bench coach David Bell manages a home game against the Astros. St. Louis ace Adam Wainwright will start in Jupiter against Houston's Mike Fiers in a 12:05 p.m. CT game that will air on Gameday Audio. Wainwright is expected to pitch three innings in what will be his second Grapefruit League start. Lefty Tyler Lyons draws the starting assignment in the 12:05 p.m. game on MLB.TV against New York's Bartolo Colon.