Arizona's right-hander scattered three hits over four scoreless innings and Arenado lifted another long ball, but their Rafters fell to the host Mesa Solar Sox, 8-4, on Wednesday afternoon.
Mesa (15-15) stands 2 1/2 back of Salt River (18-13) in the East Division. Both clubs have seven games remaining on the schedule.
Brewer pitched around a single in the second, third and fourth frames. He fanned one and threw 37 of his 53 pitches in the zone.
"Today is exactly how I expect to pitch," Brewer said. "I definitely had another [inning] in me."
The 23-year-old had yielded 12 runs -- 10 earned -- over his first three Fall League outings, which spanned 9 2/3 innings.
"Today was the first time that I really made the effort to change my speeds up a lot more," said Brewer, who sports a 5.67 ERA through seven starts. "At Double-A this year, I didn't really have to. I would rely mostly on my fastball at least one time through the lineup. ... In the AFL, I need to keep guys off my fastball. If the results tell me that's what I need to do, I will."
Specifically, Brewer threw only a handful of cutters -- his developmental pitch -- instead opting to throw his change-up to both right- and left-handed hitters. He also mixed in a curveball.
A 12th-round Draftee in 2009, Brewer broke his hand in June, but rejoined the Mobile BayBears on the diamond in August. All told, he won five of six decisions in his dozen starts, fashioning a 2.44 ERA. He said he isn't worried about getting lost in an organization that boasts Tyler Skaggs, Jarrod Parker, Wade Miley and Patrick Corbin, who are all ahead of him on the D-backs' Top 10 list.
"There's a lot of good potential in the system, but I look at it as I'm going to outwork everybody else," he said, "and I'm going to be more consistent than everybody else."
The former UCLA standout added that he hopes Arizona extends him a big-league camp invite to Spring Training. A Major League rotation spot is his aim.
Arenado, Colorado's No. 4 prospect smacked a solo shot in his first-inning at-bat off starter Cole DeVries (Twins), giving the Rafters an early edge.
"To me, personally, he is the best hitter I have seen in this league," Brewer said of his potential future nemesis. "It's crazy because he's a 20-year-old kid, but his approach is advanced."
Arenado went 2-for-4 and is batting .408 with six home runs and a league-leading 33 RBIs in 23 games.
The Solar Sox posted eight runs between the fifth and seventh innings. As part of the scoring, No. 5 Cubs prospect Josh Vitters went deep in the sixth.
Vitters -- and No. 3 White Sox prospect Brandon Short -- led all hitters with 3-for-4 afternoons.