PHOENIX — The Arizona Diamondbacks battled the Cincinnati Reds through seven tight innings before letting Sunday’s game slip away, 6-1.

Cincinnati scored five runs in the eighth inning with Spencer Steer hitting the game-opening, three-run home run off Juan Burgos. Two hits for the Diamondbacks set a season low after they scored 10 runs on Saturday.

The D-backs missed out on the chance to sweep the Reds (68-63), a team directly ahead of them in the standings, before embarking a daunting road trip to the Milwaukee Brewers and Los Angeles Dodgers.

Additionally, the Reds captured the season series in this matchup, 4-2.

“Offensively, we were held in check today,” manager Torey Lovullo said. “I keep saying on those certain days where that happens, we gotta find a way to scratch across a W.”

Arizona (64-67) played well overall during the homestand with series wins over Cincinnati and Cleveland, but that .500 record continues to elude it. The New York Mets remain 5.5 games up on the D-backs for the final Wild Card spot.

Zac Gallen duels Brady Singer

Neither offense found much success against Sunday’s starting pitchers.

Zac Gallen delivered six innings with one earned run and seven strikeouts. The lone run scored during the sixth inning on a little league home run from Noelvi Marte. Marte hit a triple and scored when shortstop Geraldo Perdomo’s throw to third base skipped off Marte’s foot.

“Gerry apologized to me, but I told him I appreciate him making the effort to try and get that guy out at third base,” Gallen said.

Otherwise, Gallen was excellent with a trio of 1-2-3 innings. In five starts during August, since he stayed put at the trade deadline, Gallen has worked a 3.10 ERA.

“ I felt like we had everything working for the most part,” Gallen said.

Reds starter Brady Singer, however, shut down the Diamondbacks after the first inning. Perdomo led off with a triple into right field and scored on a Lourdes Gurriel Jr. sacrifice fly, and from there Singer did not allow another hit through the sixth inning.

He struck out eight hitters.

Diamondbacks reliever Kyle Backhus managed to strand the bases loaded in the seventh inning, but the floodgates opened in the eighth, as the Reds sent 10 men to the plate.

Within just a few minutes, a competitive game became a blowout. Burgos was tagged with four earned runs, while Backhus was charged with one from an inherited runner.

The inning started with a line drive single from Marte that came off the bat with an odd spin. Perdomo shifted to his right and had to dive to his left, but the ball ricocheted off the end of his glove.

“That ball tried to go to left field and then went to the middle,” Perdomo said. “It was like a knuckleball.”

With one out, the Reds rallied for three straight hits off Burgos, capped by Steer’s homer.

“Things unraveled, it’s not anything you predict,” Lovullo said. “We made some mistakes in the middle of the zone, and that’s what happens.”

Arizona’s offense, meanwhile, had one base runner over the final six innings of the game.

Corbin Carroll reaches 20 steals

Corbin Carroll stole two bases on Sunday to reach 20 for the season. He became the fourth player in franchise history with three seasons of 20-plus stolen bases (Tony Womack, Chris Young and Jake McCarthy).

Carroll has hit 27 home runs and 16 triples with 20 steals this year. The only two players who previously reached those marks in a single season were Willie Mays in 1957 and Jimmy Rollins in 2007.

Diamondbacks begin gauntlet road trip in Milwaukee, Los Angeles

The Diamondbacks face the league’s best team by record in the 81-50 Brewers for four games at American Family Field, starting Monday. Without an off day, the Diamondbacks will travel back west for a three-game set at Dodger Stadium.

By opposing winning percentage, the Diamondbacks face the toughest strength of schedule in Major League Baseball for the rest of the season, and a recent run of improved play will be tested with less room for error.

“We just need to fight,” Perdomo said. “A really tough month coming up, we’re gonna play against the best teams. So for us, just try to be us, just play fun baseball … I feel we have a really good team to compete and we’re gonna do it.”

The Diamondbacks have played both teams tough this season, winning two of three games against Milwaukee back in April. They have a 3-4 record against the Dodgers with three losses by three or fewer runs.

“We’re gonna go through the gauntlet here,” Gallen said. “Just see what we’re made of, but I think everyone in here knows what’s at stake.”

Diamondbacks-Brewers probable pitchers

Monday: Eduardo Rodriguez (5.40) vs. RHP Brandon Woodruff (2.47)

Tuesday: Brandon Pfaadt (4.95) vs. RHP Jacob Misiorowski (4.19)

Wednesday: Ryne Nelson (3.63) vs. RHP Quinn Priester (3.44)

Thursday: Nabil Crismatt (1.00) vs. LHP José Quintana (3.32)

First pitch on Monday is at 4:40 p.m. MST on 98.7 and the Arizona Sports app.