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ATLANTA -- The Braves say their spring training decision to have Kris Medlen start the season in the bullpen was based on the right-hander's innings limit in his return from elbow surgery.

That decision has allowed Medlen to emerge as the most dominant starter on the staff in the most important part of the season.

Medlen struck out a career high 12 to win his sixth straight decision and lead Atlanta to a 6-1 win over the Colorado Rockies on Monday.

Medlen (7-1) allowed five hits without a walk in his second complete game of the season.

Manager Fredi Gonzalez said Medlen had the same innings limit as Washington's Stephen Strasburg.

Strasburg has thrown 156 1/3 innings and has only two more starts. Medlen has thrown only 104 innings and will be available if the Braves, the NL wild-card leader, make the playoffs.

"It was all limits to innings," Gonzalez said Monday when asked about the decision on Medlen's role. "It was basically the number that Strasburg is facing right now, 160 to 170, because they both were coming off the Tommy John surgery.

"Where do we want that 160 to 170 to end? Do we want it to end in October or do we want it to end in August?"

Medlen extended his streak of scoreless innings to 34 2/3 -- the Braves' longest since Greg Maddux in 2000 -- before the Rockies scored an unearned run in the seventh. He threw 111 pitches, including 85 strikes.

"He was terrific," said Colorado manager Jim Tracy. "And he's been terrific for a while.

"He had three pitches for strikes whenever he wanted them. Unfortunately, with the way he's been throwing the ball, we pretty much put him in a rocking chair right from the outset."

Medlen appeared in 38 games in relief before moving into the rotation on July 31. He is 6-0 with a 0.54 ERA in seven starts. He spent most of 2011 on the disabled list recovering from elbow ligament-replacement surgery on Aug. 18. 2010.

Medlen was 5-0 as a starter in 2010. The Braves have won his last 18 starts.

Medlen said adding a curveball as a starter has been "huge."

"You can just attack guys so differently with an extra pitch, an effective pitch, too," he said. "I got a couple strikeouts with it."

Medlen said he is glad he doesn't have to worry about an innings limit, but he noted pitching in relief "was not easy on your arm."

"You're not throwing as many innings, but you're getting up and warming up just as much as anybody," he said. "I love the starting part because you can get four days to prepare your arm."

David Ross hit a two-run double in Atlanta's four-run third inning.

Rockies starter Tyler Chatwood (4-4) gave up six runs, five earned, in only three innings. Chatwood allowed only three hits but was hurt by five walks, matching his career high.

Chatwood loaded the bases with three walks in the third. Martin Prado drove in Michael Bourn with a flyball to centerfield. Juan Francisco's single drove in Jose Constanza. Ross added a two-run double for a 6-0 lead.

Two walks and a wild pitch by Chatwood and two errors on one play by first baseman Jordan Pacheco helped the Braves score two runs in the first. After walks to Bourn and Freddie Freeman, Bourn scored from third on a wild pitch. Prado hit a sharp grounder off Chatwood's left leg. Pacheco couldn't handle Chatwood's throw to first base, and Pacheco then made a wild throw to third base for another error, allowing Freeman to score.

Prado was awarded a hit on the play in a scoring change after the game.

A throwing error by shortstop Paul Janish helped the Rockies score an unearned run in the seventh inning, the first run allowed by Medlen since Aug. 11.

Carlos Gonzalez singled and scored from first when Janish dove for Pacheco's grounder and threw wild to second base for an error. Pacheco advanced to third on his single and Janish's error, but Medlen struck out Tyler Colvin and Chris Nelson to end the inning.

Medlen's streak of scoreless innings was the longest for a Braves pitcher since Maddux did not allow a run in 39 1/3 consecutive innings from Sept. 2-28, 2000.

Prado made his second straight start at second base. Gonzalez has benched All-Star Dan Uggla, who is hitting only .208.

Game notes

Pacheco has a 12-game hitting streak. ... Medlen's previous career high was nine strikeouts. ... RHP Randall Delgado, recalled from Triple-A Gwinnett, will pitch out of the Braves' bullpen. The Braves announced after the game RHPs Julio Teheran and Cory Gearrin will join the team on Tuesday. ... C Brian McCann, who had a cortisone shot in his right shoulder after Saturday's game, missed his second straight start. ... Rockies SS Troy Tulowitzki, on the 15-day DL with a groin injury, played as a DH on Monday with Triple-A Colorado Springs and is scheduled to play shortstop with Double-A Tulsa Wednesday and Thursday. ... Braves RHP Tommy Hanson will try for his 13th win against Colorado LHP Drew Pomeranz (1-8) on Tuesday night.