DENVER -- Colorado Rockies manager Walt Weiss had a moment of concern Monday when Chad Bettis threw his first three pitches for balls. At that point, a two-hit shutout seemed far, far away.

Bettis was starting on seven days of rest against the slumping San Francisco Giants, and Weiss could only wonder if three additional days of rest were going to work against Bettis.

"It crossed my mind," Weiss said, "but he was all good from there on."

Indeed, Bettis got 15 ground-ball outs in the Rockies' 6-0 win. He struck out seven, didn't issue a walk and threw 103 pitches, 73 strikes, while throwing his first career complete game and the Rockies' first of the season.

Carlos Gonzalez hit a grand slam and Nick Hundley homered as the Rockies packed all their runs into the third inning against Giants starter Matt Moore, who pitched a season-low 2 2/3 innings.

Bettis' complete-game shutout was the first by a Rockies pitcher at Coors Field since left-hander Chris Rusin threw a five-hitter Aug. 16, 2015, against the San Diego Padres. It was the 29th complete-game shutout at Coors Field and the 13th by a Rockies pitcher.

"I didn't really think about it," Bettis said of the complete game. "I was really trying not to focus on that and just (on) going down the order."

Bettis' previous longest outing was 8 1/3 innings against the Giants on May 24, 2015. He retired the first 14 batters he faced Monday before Eduardo Nunez singled to left with two outs in the fifth. Bettis (12-7) then got Brandon Belt to roll a grounder to second.

Bettis gave up a leadoff double to Trevor Brown in the sixth but then retired the final 12 batters he faced, allowing one ball to be hit out of the infield in that span. The only other outfield putout came in the fourth when Denard Span flied to center. No runner reached third base against Bettis, and Brown was the only one to get to second.

"His angle was really good, his fastball was really downhill," said Hundley, the Rockies' catcher. "I know he's been working on that the last couple bullpens. His depth was outstanding. You could tell by the soft contact on the ground we were getting."

Bettis' two-hit shutout was fifth in Rockies history and second at Coors Field. Jeff Francis threw the other on July 24, 2006, against St. Louis. Jason Marquis was the last Rockies pitcher to throw a two-hit shutout; it was on the road against the Los Angeles Dodgers on June 30, 2009.

Bettis called it his best game. Asked if he had the best stuff of his career, he said, "Maybe not the best stuff, but the best feel for stuff."

The Rockies improved to 4-3 on their current homestand with their sixth win in nine games.

The loss was the fifth in seven games for the Giants, whose 16-31 record since the All-Star break is the worst in the majors. That slide includes 18 losses in 25 road games.

"We couldn't generate anything," Giants manager Bruce Bochy said. "Their guy pitched great, I'll give him that. But at the same time, we've been in this for a little while, and it's time for us to wake up here. That was a tough one. We had quick outs, soft outs."

Gonzalez's grand slam highlighted the third-inning explosion. It was his sixth career slam and second this season. Gonzalez is tied with Dante Bichette and Andres Galarraga for the second-most grand slams in franchise history behind Todd Helton (seven).

The Rockies loaded the bases with no outs on walks to Cristhian Adames and Bettis and a single by Raimel Tapia that went off the glove of shortstop Brandon Crawford.

DJ LeMahieu's sacrifice fly got a run home and moved up the other two runners. After Nolan Arenado was intentionally walked, so the left-handed Moore could face the left-handed-hitting Gonzalez, the Colorado right fielder belted his 25th homer of the season. Gonzalez said he was not surprised by the strategy to pitch to him.

"They have a tough lefty on the mound, and Nolan is leading the league in RBIs," said Gonzalez, who hit the ball hard with nothing to show for it Sunday while going 0-for-5, leaving him with five hits in his past 46 at-bats. "I'm having a hard time to get hits, so I think they took their chances and it didn't work. Good for us, bad for them."

Two batters later, Hundley hit his 10th homer and his fifth in 10 games to make it 6-0.

"I think I'm a lot more relaxed," Hundley said. "Feel comfortable in the box, really calm. Anytime you're relaxed and comfortable in there, you got a chance to be successful."

NOTES: Giants LHP Ty Blach, who grew up in the Denver area, pitched three scoreless innings in his major league debut, four days after the Giants recalled him from Triple-A Sacramento. ... Rockies LF Ryan Raburn left the game in the sixth inning with a left foot contusion and was listed day-to-day. ... RF Carlos Gonzalez has hit 25 or more homers in five seasons with the Rockies, tied for the third most in club history with Dante Bichette and Larry Walker and trailing Todd Helton (seven) and Vinny Castilla (six). ... Giants C Buster Posey did not play after going 1-for-16 at Wrigley Field and playing all four games. Manager Bruce Bochy said Posey likely will play first base Tuesday. ... Rockies CF Charlie Blackmon did not play for the third straight day due to lower back stiffness.