Fielder homered in the sixth off Rob Wooten with Shin-Soo Choo aboard.
"The past two or three days he is starting to be more consistent with his swing, starting to feel better at the plate," Rangers manager Ron Washington said. "You could even see the difference in BP. He's just spraying the ball around and using his hands well. I hope he continues."
Scheppers, who has made 115 relief appearances in the majors but is in the mix for a rotation slot, gave up two runs in the first on three hits, including Ryan Braun's RBI double. Scheppers settled down after that, retiring 16 of the final 18 batters he faced, striking out six and without walking a batter.
"He did a great job," Washington said. "(Carlos) Gomez ambushed him with a fastball (leading off the game). Then he got Braun into a pretty good count and just hung a breaking ball. After that he put up five zeroes, (throwing) in and out, up and down, changing speeds."
Yovani Gallardo, who earned his fifth opening day assignment for the Brewers, gave up four runs -- three unearned thanks to two errors by Mark Reynolds and another by Lyle Overbay. Gallardo allowed eight hits, and struck out four in 5 1/3 innings.
Braun, who missed the previous two games with an illness, is hitting .458 in 11 games.
The Brewers committed five errors, which led to six unearned runs.
Leonys Martin went 3 for 4 for the Rangers with a double, scored a run and drove in a run.