ATLANTA(AP) Aaron Cook kept throwing sinkers, and his infielders kept making plays.

Cook pitched a four-hitter and Todd Helton 's grand slam ended Colorado's power slump as the Rockies beat the Atlanta Braves 9-0 on Thursday night.

Cook (3-1) retired the final 16 batters for his second career shutout. He had 20 groundouts and did not allow a baserunner to advance past second for his first win in eight career starts against Atlanta.

''I didn't need to show up today,'' said Rockies catcher Chris Iannetta of his easy task of calling pitches for Cook. ''The choice was between a sinker and a sinker. ... It was the best sinker I've seen this year.''

Jeff Francoeur singled with two outs in the fourth and then Cook retired everyone else. The only other hits that Cook gave up were a single to Chipper Jones in the first and back-to-back singles by Francoeur and Jordan Schafer in the second.

''When he's got that sinker with that late movement, it's every bit as good as it gets in this game,'' said Braves catcher Brian McCann . ''He baited us and made us swing at tough pitches.''

Colorado second baseman Clint Barmes had 10 assists.

''I was cheering for the guys making the plays,'' said Cook of his infielders. ''I was throwing strikes, keeping the ball down. ... I always take a lot of pride in our defense.''

The Rockies had gone four games - and 46 innings - with a homer before Helton's shot in the fourth inning. Before that mini-drought, the Rockies had not had as many as two straight games without a homer this season.

The Rockies posted only their second shutout of the season. The only other one was a 3-0 victory over Arizona in the second game of the season.

Helton had three hits and drove in five runs as the Rockies spoiled Kris Medlen 's major league debut.

Medlen (0-1) gave up five runs in three innings. He left after facing four batters in the fourth.

The Rockies recovered after losing games Wednesday and Thursday by the combined score of 20-5.

''We definitely needed this one, no doubt about that, especially after the way we got beat last night,'' said Helton of the Braves' 12-4 win on Wednesday night.

Helton, who opened the series with his 2000th career hit Tuesday night, helped give the Rockies a split of the four games with another memorable game. He enjoyed his 10th career game with five RBIs while hitting his fifth career grand slam, his first since Sept. 10, 2006 against Washington.

The 23-year-old Medlen earned his promotion by posting a 5-0 record with a 1.19 in eight games with Triple-A Gwinnett near Atlanta. His major league debut included two wild pitches, a hit batter, a balk and five walks - all while recording only nine outs.

''I can't explain it but whatever it was, it's unacceptable,'' Medlen said. ''I felt fine. I can't explain what happened. ... The wheels fell off.''

After Medlen's second wild pitch far outside the reach of McCann in the fourth inning, manager Bobby Cox and assistant trainer Jim Lovell hurried out to the mound. Cox said he was concerned that a drop in the velocity of Medlen's pitches was a sign the right-hander was injured.

Medlen remained in the game, but he walked Clint Barmes on four pitches to load the bases with no outs. Braves pitching coach Roger McDowell visited Medlen, who then hit Cook's left elbow with a pitch, forcing in a run.

Cox returned to the mound to pull Medlen.

Reliever James Parr almost stranded the three runners he inherited. After recording outs on popups by Dexter Fowler and Troy Tulowitzki , Parr gave up the grand slam to Helton on a 3-2 fastball to give Colorado a 6-0 lead.

''When the count was 3-2, I said 'This kid's in trouble, he's got to throw a strike to get him out,''' said Clint Hurdle of Parr.

Helton's homer was just beyond the reach of Francoeur, who had to look in his glove to see he didn't make the catch.

''The wind was blowing pretty good, and the ball barely got out,'' Helton said.

Helton drove in Dexter Fowler with a sixth-inning double off Parr.

Notes: Helton drove in a career-high six runs on May 23, 2003 against Los Angeles. ... The Braves placed IF Omar Infante (broken left hand) and LHP Jo-Jo Reyes (right hamstring) on the 15-day disabled list and called up IF Diory Hernandez with Medlen from Triple-A Gwinnett. Hernandez entered the game in the seventh, marking the first time since Sept. 5, 2001 ( Tim Spooneybarger and Cory Aldridge ) the Braves had two players make their major league debut in the same game.