DENVER (AP) — Ian Stewart hit a third-inning grand slam in his ninth career at-bat — one of four Colorado home runs — and the Rockies overpowered the Pittsburgh Pirates 9-2 on Tuesday night.

Matt Holliday, Troy Tulowitzki and Brad Hawpe also homered for the Rockies, who closed to within 2 1/2 games on NL wild-card leaders San Diego and Philadelphia.

Tony Armas (2-4) retired the first six batters he faced before Yorvit Torrealba and Jamey Carroll led off the third with singles. After pitcher Elmer Dessens put down a successful sacrifice bunt, Ryan Spilborghs walked and Stewart drove a 2-1 pitch to left to make it 4-1.

Stewart, who was called up from Triple-A Colorado Springs on Aug. 11, is the third rookie this year to hit a grand slam for his first major league homer. Houston’s Hunter Pence did it May 5 at St. Louis, and Danny Richar of the Chicago White Sox did it Friday at Toronto.

The Rockies loaded the bases again in the third, but Armas got out of the jam without allowing a run. He gave up seven runs and eight hits in 4 1-3 innings, walking three and striking out four.

The Rockies scored three times in the fifth on Holliday’s solo homer and Torrealba’s bases-loaded single, which scored Todd Helton and Tulowitzki and chased Armas from the game.

Taylor Buchholz (6-4) got the win in relief of Dessens. Buchholz came on two on and two out in the fifth and got Jason Bay to pop out to third. He retired nine of the 10 batters he faced.

Tulowitzki, who homered and tied his career high with four hits on Monday night, hit his 17th of the year off Shane Youman in the seventh. Hawpe followed with his 22nd, making it 9-2.

The Pirates scored on Nate McLouth’s eighth home run of the year to lead off the third. He scored again on a groundout in the fifth.

Notes: The four homers was a season-high for Colorado. ... The Rockies have hit seven grand slams this season, extending the club record for a single season. ... McLouth has hit safely in 17 of his last 19 games. ... Stewart is the second player in Colorado history to hit a grand slam for his first homer. Jim Tatum accomplished the feat at Wrigley Field in Chicago on May 4, 1993.