SAN FRANCISCO – In his first time throwing off a mound in nearly six weeks, Braves reliever Jonny Venters had discomfort in his troublesome left elbow and cut short the planned 15-20 pitch session Thursday.

“Just didn’t feel very good,” said the left-hander, who got a platelet-rich plasma injection from Dr. James Andrews on April 2, in hopes of avoiding surgery on the elbow he injured in the last week of spring training.

After following the doctor’s orders not to throw for four weeks to allow the cutting-edge medication to take effect, Venters resumed a flat-ground throwing program on April 30 and was encouraged by how his elbow responded to those gradually increased sessions.

But when he got on the mound Thursday at AT&T Park, he felt something in the elbow and stopped after 10 or 11 pitches.

“Just a little tender,” he said. “We’ll see how it feels tomorrow, how it responds.”

Venters was asked if thought perhaps it was discomfort caused from moving up from flat-ground throwing to the additional slope of throwing on the downhill slope, along with throwing a little harder from the mound.

“You’re putting new stress on it, different stress than you are when you throw flat ground,” he said. “Might be one of those things where you’ve just got to get used to throwing off that mound again. It didn’t feel great, but see how it feels tomorrow.”

“I was putting something on it, for sure. Ball’s still coming out (of his hand) decent, just didn’t feel very good. So we’ll see.”

Venters had “Tommy John” elbow surgery after the 2005 minor league season to reconstruct a torn ulnar collateral ligament in his pitching elbow. Andrews, considered one of the world’s leading practitioners of the surgery, did that procedure on Venters.

With pitchers who’ve had Tommy John surgery before, MRI exams on the elbow years later can be unclear because of scar tissue or other factors where the ligament was replaced. Such was the case with Venters in April, and Andrews recommended the PCP injection and four weeks of rest in hopes it would take care of the situation.

Venters was an integral part of a bullpen rated among baseball’s best in recent years. The 28-year-old lefty had 230 appearances in his first three major league seasons through 2012, including a majors-leading 85 in 2011, when he had a 1.84 ERA and a stingy .176 opponents’ batting average.

Over the past three seasons, Sean Marshall (231) was the only major league pitcher with more appearances than Venters, who had a career-high 3.22 ERA in 66 appearances last season. He pitched much better after returning from a July stint on the disabled list for elbow inflammation, posting a 1.71 ERA in his final 26 appearances.