DENVER — After the worst start of his brief major league career, Braves pitcher Brandon Beachy did not make any excuses. Even when he had a ready-made one that his manager used for him.

Coors Field.

Beachy gave up a three-run homer in the first inning and a two-run homer in the second and didn’t make it out of the fifth inning of Tuesday’s 12-3 loss against the Rockies in his first start at Coors Field.

“They have to experience it,” Braves manager Fredi Gonzalez said of first-timers pitching in the thin air of mile-high Coors Field. “They really do.”

The loss was the fifth in 18 games for the Braves and snapped a five-game winning streak against the Rockies this month. They swept a four-game series from Colorado at Turner Field.

Beachy (3-2) gave up six runs, nine hits and a career-high five walks in 4 2/3 innings, but insisted the ballpark wasn’t the reason. He pitched on 10 days’ rest — more than twice the usual because of the All-Star break — but didn’t mention the layoff.

“I don’t think this place had anything to do with it,” Beachy said of Coors Field, where the spacious outfield contributes to bloop singles, and the wide gaps are a haven for doubles and triples. “I struggled with my slider in Philadelphia [July 8] and again today.”

Beachy gave up as many runs (six) in the first three innings as he allowed in 30 innings in his previous five road starts this season. He had been warned by other pitchers that sliders tended not to slide as much at high altitude.

“I think he learned from it and starting throwing the change-up a little bit more than he did the breaking balls,” Gonzalez said. “I think it’s a good experience.”

Beachy was 2-0 with a 1.80 ERA on the road before Tuesday, when he gave up a three-run homer to Troy Tulowitzki in the first inning and a two-run homer to Carlos Gonzalez in the second. Both were on hanging sliders.

Beachy issued one more walk in 4 2/3 innings than he had in all his other road starts combined this season. He’s known for his pinpoint command and had more than two walks in only three of his 15 career starts before Tuesday.

“I struggled with my fastball early, especially away to lefties,” he said. “I was leaving it a couple of inches off the plate, and he wasn’t giving me that, and I just kept going there. Didn’t make that adjustment.”

Rough stretch for Gearrin

The Braves like reliever Cory Gearrin’s potential, but the rookie sidearmer is going to have to do something different to become effective against left-handed hitters.

After giving up four earned runs in the sixth inning of Tuesday’s loss, Gearrin has a 13.50 ERA in his past 10 appearances. He has been charged with 13 hits, 13 runs and nine walks in 8 2/3 innings in that span.

Lefty batters have hit .393 (11-for-28) with a .514 OBP against Gearrin, who has limited right-handers to .143 (6-for-42) with a .260 OBP.

“He’s had a difficult time getting left-handed hitters out,” Gonzalez said. “We need to get him to throw something else, a change-up or something, to get those left-handers off that fastball.”

Proctor’s struggles

The Braves have waited for most of two seasons for Scott Proctor to return to form, and the veteran reliever just hasn’t been able to do it, at least not over a significant stretch. After two elbow surgeries, he hasn’t regained consistent command and movement on his pitches.

Proctor gave up three hits and the last two of the Rockies’ runs Tuesday, giving him a 10.45 ERA in his past 12 appearances. In 10 1/3 innings over that period, he has allowed 16 hits, 12 earned runs, four homers, six walks and a .356 opponents’ average.