DENVER -- A minor mechanical adjustment paid off in a huge way Sunday for Kyle Freeland.

The Colorado rookie left-hander pitched seven scoreless innings as the Rockies completed a three-game sweep by pounding the slumping San Francisco Giants 8-0.

Making his fourth career start, Freeland (2-1) held the Giants to six hits with one walk and three strikeouts. He retired the first 11 batters he faced, didn't allow a runner to get past first until the fifth inning and got 12 outs on ground balls.

"His best stuff is down in the strike zone with movement down," Rockies manager Bud Black said. "When you're throwing the ball in the low 90s with action down, you're going to get grounders."

Gerardo Parra hit a two-run homer and had three RBIs for the Rockies, who put the game out of reach with a five-run sixth. Charlie Blackmon and Trevor Story each drove in two runs.

The win gave the Rockies their first three-game sweep of the Giants at Coors Field since May 24-26, 2002. The Rockies, who outscored the Giants 26-8 in the series, are 6-1 against San Francisco this season.

Colorado (13-6) earned its sixth win in seven games. Only twice previously did the Rockies post a better 19-game record to start a season.

The Giants have lost four straight games and six of their past seven, dropping their record to 6-13, their worst start since 1983.

San Francisco starter Jeff Samardzija (0-4) gave up seven hits and seven runs in 5 1/3 innings. Samardzija, Johnny Cueto and Matt Moore, the three starters the Rockies beat in the series, combined to work just 14 1/3 innings in the series with an 11.93 ERA. Giants starters are last in the majors with a 5.02 ERA, and ace Madison Bumgarner is sidelined with a sprained left shoulder after a dirt bike accident in Colorado on Thursday.

"Right now, there is nothing clicking," Giants manager Bruce Bochy said. "Let's be honest, it's been a rough start, and we're not very good right now. I am not saying we're not good; we are good. But we have to find a way come out of this by all of us stepping it up. But this was a tough way to end this series the way the first two games went.

"We've been through it. We just have to find a way to get through this, and they will."

Freeland was coming off a shaky start at Los Angeles. In that game, he allowed only one hit but put 10 Dodgers on base, including the two batters he faced in the fifth before leaving with a 4-1 lead but failing to qualify for the victory in Colorado's 4-3 win. In that outing, he threw 45 of 87 pitches for strikes.

In his side session before this start, Freeland worked on a slightly straighter alignment with his front foot toward home plate and having his head get down the slope of the mound and not pull off.

"That worked well today," Freeland said. "Even when I felt myself get out of that tunnel and not be directly down the mound like I should, I felt I noticed it. (Catcher) Tony (Wolters) noticed. He either let me know or I could feel it and I immediately made the adjustment."

Freeland struck out Brandon Crawford to end the sixth with runners on first and second. He got Crawford to flail at a 3-2 slider on his 93rd and final pitch, his 57th strike.

"A strike-to-ball (pitch)," Freeland said. "It started on the outer half of plate. We knew he'd be looking out there."

Blackmon led off the first with a triple to right-center, and he scored on Nolan Arenado's sacrifice fly. Parra homered with two outs in the fourth, cranking a flat 1-1 split-finger pitch over the fence in right for his second homer and scoring Carlos Gonzalez, who had walked.

The Rockies blew the game open in the sixth. Parra hit a run-scoring double, and Story's two-run single chased Samardzija, who matched his shortest start of the season with 5 1/3 innings. Blackmon drove in two runs with an opposite-field double to left off Steven Okert.

Scott Oberg and Chris Rusin each threw a hitless inning to complete Colorado's shutout.

NOTES: San Francisco's Brandon Belt, the team's regular first baseman, made his first start in left field since July 3 at Arizona. ... Giants RF Hunter Pence returned to the lineup and went 2-for-3. He pinch-hit Saturday after twisting his knee Friday. ... Giants OF Mac Williamson (strained left quadriceps) began a rehab assignment Saturday with Triple-A Sacramento and went 0-for-4 with two strikeouts. ... San Francisco 3B Eduardo Nunez hit leadoff for the first time this season with CF Denard Span unavailable after suffering a mild right shoulder sprain Saturday night. ... Rockies CF Charlie Blackmon extended his hitting streak to eight games, going 2-for-3. ... Rockies RHP Antonio Senzatela, who is 3-0 with a 2.08 ERA, is the third pitcher in club history to go 3-0 or better with an ERA under 3.00 in his first four career starts with the team.