Freeland (9-6) allowed five hits while striking out five, walking three and hitting a batter. Colorado's starting pitching is 6-0 with a 1.65 ERA at Coors Field in July.
Ian Desmond and Garrett Hampson also drove in runs for the Rockies, who have won 14 of 19 this month. Adam Ottavinothrew a spotless ninth for his fourth save of the year. Usual-closer Wade Davis had pitched in Colorado's last two games.
Sean Manaea (9-7) allowed three runs on nine hits for the A's, who had their season high-tying, six-game winning streak snapped. It was Manaea's first loss since May 30.
The Rockies used small ball to take the lead against Manaea in the second. Noel Cuevas bunted aboard to start the inning and was later brought home on a squeeze bunt from Hampson.
Desmond made it 2-0 with an RBI single in the fifth but was thrown out trying to reach second. Arenado followed with his 26th home run of the season and 100th career homer at Coors Field.
Freeland managed to keep Oakland scoreless through six innings despite heavy traffic on the bases. The Denver native forced Matt Olson to line out to second to end a bases-loaded threat in the first, then induced a double play to get out of another bases-loaded jam in the fifth.
The A's finally got on the board as Jed Lowrie hit an RBI double off reliever Bryan Shaw in the seventh. They loaded the bases for the third time in the game in the eighth before Scott Oberg struck out Matt Chapman to end the inning.
Rockies: OF David Dahl (broken foot) was reinstated from the 10-day disabled list and optioned to Triple-A Albuquerque. . LHP Mike Dunn (left shoulder joint inflammation) was transferred from the 10-day disabled list to the 60-day DL.
OH, NO SHOW
RHP Seunghwan Oh, acquired by the Rockies in a trade with the Blue Jays on Thursday, was not available Friday because of travel issues.
HE'S BACK, BABY
The Rockies activated RHP German Marquez from the paternity list and optioned OF Raimel Tapia to Triple-A Albuquerque. Marquez, who was in Venezuela for the birth of his son earlier in the week, will pitch in Sunday's series finale.
WE MEET AGAIN
Arenado and Chapman played together at El Toro High School in Southern California in 2009. Arenado was a highly touted shortstop in his senior year and Chapman was his backup.
Athletics: LHP Brett Anderson (2-2, 5.46 ERA) allowed two runs in six innings in a win at Texas on Monday, only the second time in his last seven outings that he went six.
Rockies: Antonio Senzatela (3-3, 5.55) struggled in his first start since coming off the disabled list, allowing four runs over 5 1/3 innings in Sunday's loss in Arizona.