ATLANTA — On a day when he was going to start, Jeff Karstens started out in the Pittsburgh bullpen.

He wasn’t there long.

Karstens entered in relief after the pitcher who replaced him in the rotation, Charlie Morton, left the game with a tight left hamstring. The former starter gave up only one run in 4 2-3 innings, leading the Pirates past the Atlanta Braves 3-2 on Wednesday night.

“I did what I had to do to save the bullpen,” Karstens said. “I’m used to throwing a lot.”

Adam LaRoche had two RBIs and Craig Monroe pulled off some nifty baserunning to score a crucial run for the Pirates, who snapped a three-game losing streak and denied Atlanta its first four-game winning streak of the season.

Morton was called up from Triple-A Indianapolis to start against his former team, but the Pirates right-hander lasted only one inning. Karstens (3-4) took over and didn’t allow a run until the sixth.

Asked if he expected to be called in so soon, Karstens quipped, “I don’t think my arm expected it.”

LaRoche put the Pirates ahead in the third against Jair Jurrjens (5-4), driving in a run with a forceout. Jason Jaramillo made it 2-0 with a two-out single.

After Atlanta closed to 2-1 on a near-homer by Brian McCann, Monroe’s heads-up play on the base paths restored the two-run lead. He led off the seventh as a pinch-hitter and was grazed by Eric O’Flaherty’s pitch. Monroe moved up on a groundout and was still at second with two outs when LaRoche hit a hard shot up the middle.

Second baseman Kelly Johnson made a diving stop and flipped to shortstop Yunel Escobar, trying for a force at second. The toss was late and Monroe never stopped, streaking around third while Escobar held the ball, not bothering to look toward the runner.

His delayed throw home was wild, and it wouldn’t have gotten the speedy Monroe anyway.

“It wasn’t heads-up,” Braves manager Bobby Cox said, “and I don’t know if anybody was yelling to tell him.”

Escobar hustled out of the clubhouse after the game without speaking to reporters, leaving behind his teammates to explain what happened.

“He was probably assuming (Monroe) couldn’t score,” Johnson said. “Usually when you have the ball, you peek in to see where the runners are.”

Matt Capps pitched the ninth for his 14th save, giving up a two-out homer to Garret Anderson.

Escobar, who had the game-winning hit Tuesday, doubled in the sixth and came around to score on McCann’s towering drive to left-center. The ball struck the top of the wall, bounced back into play and was ruled a double by the umpiring crew.

Cox came out to question the call, and three umpires headed down a tunnel next to the Pirates dugout for the first video review in Turner Field history. They only needed about a minute to decide the call was right.

“It was real close, close enough to give it a look,” said McCann, who thought from the crowd’s reaction that he had hit a game-tying homer.

While both teams managed only six hits, the Pirates had plenty of chances. Atlanta walked seven and hit two batters, but Pittsburgh left the bases loaded three times.

Brandon Moss comes up twice in those situations, striking out in the first and grounding out in the seventh. Pinch-hitter Eric Hinske took a called third strike with the bases full in the ninth.

Morton got through the first, allowing one hit, but he headed straight to clubhouse after the inning. The Pirates said his hamstring tightened before the game and he couldn’t pitch through it.

“It’s very disappointing,” said Morton, who was listed as day to day. “I was anxious to get back to Atlanta and get in some quality innings.”

Morton was one of three prospects traded by the Braves last week for All-Star center fielder Nate McLouth. The right-hander was called up after Karstens, initially listed as Wednesday’s starter, pitched in relief during Monday’s 15-inning loss to the Braves.

“The guy has a rubber arm,” LaRoche said. “When he’s on, he’s dangerous.”

Jurrjens went six innings, giving up four hits and two runs while striking out seven. This was the sixth time in 13 starts that Atlanta has scored two runs or less.

“It’s just a little frustrating,” Jurrjens said. “This was a big game for us, and we let it get away.”

NOTES: The Braves have five three-game winning streaks this season. … Greg Norton made his second straight start at first base for Atlanta and wound up falling over the mound after leaping to cut off a throw to the plate in the third. … LaRoche has reached base safely in 20 of his last 23 games.