PITTSBURGH -- Jonny Venters thought he had given up a tying home run with two outs in the bottom of the ninth inning.
"It sounded loud," the Atlanta Braves' reliever said. "I thought it was gone."
Gregory Polanco's drive to right field hit off the top of the 21-foot wall, however, and he was held to a double.
Polanco was disappointed his drive did not clear the high wall.
"It's unbelievable, man," he said. "I hit the ball really hard. It's PNC (Park), man. Every other park, that's a homer."
Acuna hit the fifth pitch out to left-center off Trevor Williams. It was the rookie's 20th homer and sixth leading off the first inning, including four in the last two weeks.
"He's so exciting," Teheran said. "You expect him to hit a long ball every time he comes up."
The NL East leaders went ahead 2-1 in the eighth when Freeman, who leads the league in hitting, sent a fly ball to deep left field off Edgar Santana. That came after Atlanta loaded the bases against Kyle Crick (2-2), who did not retire any of the three batters he faced.
"You'd love to score five or six runs every night, but that's not always going to happen," Freeman said. "These are the types of games you have to win in a pennant race. It's a really good win for us."
Atlanta moved three games ahead of the second-place Phillies, who lost 8-7 at Washington.
Freeman's sac fly made a winner of Teheran (9-7), who allowed one run and two hits in seven innings while striking out five and walking one. Teheran is 2-0 with a 2.93 ERA in his last five starts.
Atlanta also mustered only three hits but won for the 17th time in 25 games.
It was seven years to the day since Venters converted his last save for the Braves on Aug. 22, 2011, at the Chicago Cubs. The left-hander missed five major league seasons from 2013-17 while recovering from three Tommy John operations. He returned this year with the Tampa Bay Rays.
The Braves acquired Venters in a July trade and he got his first opportunity to fill in for injured closer A.J. Minter (lower back tightness) on Wednesday.
"I told Jonny I might be using him in some save situations and he was ready," Braves manager Brian Snitker said.
The Pirates got their run in the fifth when Colin Moran broke up Teheran's no-hit bid with a two-out RBI single. Pittsburgh's only other hit was a two-out single by Cervelli.
The Pirates have scored just 16 runs in their last 10 games, going 2-8.
Williams had another strong outing, permitting one run and two hits in six innings, but again was hurt by a lack of run support. Williams' ERA is 0.97 ERA in six starts since the All-Star break, yet his record is just 3-2. He is also 1-2 in four August starts despite a 1.44 ERA.
"He's pitched so well, and he pitched so well again tonight," Pittsburgh manager Clint Hurdle said. "It was just fun to watch him out there like a kid in the backyard going to work."
Braves: C Kurt Suzuki (bruised left triceps) was out of the lineup after being hit by a pitch but is not expected to go on the disabled list. C Chris Stewart was called up from Triple-A Gwinnett to serve as a backup, and OF Michael Reed was optioned to the Stripers.
Pirates: RHP Chris Archer (left leg discomfort) is listed as the scheduled starter Sunday at Milwaukee. He left his start Monday night against Atlanta after four innings. ... 2B Josh Harrison (strained left hamstring) did not start for a third straight game but struck out as a pinch-hitter. ... INF-OF Sean Rodriguez (strained left abdominal muscle) is likely to begin a rehab assignment in the next few days. ... SS Jordy Mercer (strained left calf) took batting and fielding practice. ... INF Jung Ho Kang (left wrist surgery), on the disabled list at Triple-A Indianapolis, has been cleared to begin gripping exercises.
TRICK SHOT ARTIST
Braves second baseman Ozzie Albies hit a foul ball in the seventh inning that rebounded off the netting behind home plate and struck him on top of his batting helmet.
TURN BACK THE CLOCK
The Braves announced their weeknight and Sunday afternoon home games will begin 15 minutes earlier next season at 7:20 p.m. and 1:20 p.m., respectively.
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