CINCINNATI -- With the first four spots of the 2020 Reds rotation likely spoken for already, the battle for the fifth spot next spring could become quite the donnybrook. Unlike other potential contenders -- inside or outside the organization -- Tyler Mahle can use the rest of the 2019 season to make his case as a starter.

It didn’t go too well for Mahle during a five-run top of the fifth inning Friday during a 7-5 Reds loss to the D-backs at Great American Ball Park. The right-hander lasted only 4 1/3 innings on 92 pitches as he gave up five earned runs on six hits and two walks with three strikeouts. But it was a homer allowed in the pivotal fifth that stung the most.

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“For the most part, I really think it was a good night,” Reds manager David Bell said. “It didn’t end the way he wanted it to, but up until that point, it was solid.”

Cincinnati had a 1-0 lead in the third when Mahle’s 2-2 pitch to Nick Ahmed was hit to center field for a homer to lead off the inning. As part of his four-RBI game, Eugenio Suarez put Mahle back in the lead with his RBI single in the bottom of the third.

Setting the stage for a big Arizona rally in the fifth, Carson Kelly lined a single to center field. Next, in a sacrifice situation, Arizona starter Robbie Ray made a risky two-strike bunt attempt. He was trying to get it to the left side of the infield, but instead lofted it in the air into no-man’s land behind the mound for a single. 

That set up Ketel Marte, who jumped all over a high 0-2 pitch for a three-run homer to right field.

“I think there was an easy way out of it, and it was to throw a split there to Marte,” Mahle explained. “I was thinking it in the back of my head. Curt [Casali] called a cutter up and in. I went with that and was comfortable with it. I think if I had gone with my gut feeling, it would’ve been a different outcome. Also, it was 0-2 and I threw a cutter in the zone. It wasn’t a terrible pitch. It was supposed to be up and in, but it should’ve been off [the plate] and something he wouldn’t be able to hit. So, two mistakes in one pitch cost me three runs.”

Wilmer Flores added a double, bringing Mahle’s night to a close. Two more runs scored in the inning with Lucas Sims on the mound.

Luis Castillo, Sonny Gray, Trevor Bauer and Anthony DeSclafani appear to be locked in as the first four starters for the Reds next season. The fifth spot seems up for grabs among Mahle, Kevin Gausman, Sims and Sal Romano, among others. Gausman, claimed off waivers last month from the Braves, is intriguing because he’s capable of reaching into the high 90s with his fastball velocity. The front office could also look around the free-agent and trade markets, but there is less pressure this winter after a big rotation overhaul last offseason.

Mahle -- on the other hand -- was a prospect the organization developed -- including his two-plus seasons in the Majors. He returned from Triple-A Louisville on Sunday to make a start and seemed destined for a bullpen spot the rest of the way in 2019. But with soon-to-be free agent Alex Wood out once again with a back injury, Mahle is in line for more starts.

“I’m using every opportunity I get to start and put some good starts together,” Mahle said. “I think if we stay on a five-day [rotation] and I make all my starts, I think I have four more. I want to make the most of it.”

Sunday’s start went well for Mahle, who delivered 6 1/3 innings with two hits and two runs (one earned) allowed, but he was the victim of a blown save in a loss to the Cardinals.

Bell remained bullish on Mahle, instead offering effusive praise despite his overall record being less than rosy at 2-11 with a 4.94 ERA in 21 starts, including having gone 0-6 with a 5.75 ERA over his last 10 big league starts. That includes a one-month interruption on the injured list with a left hamstring strain.

“For Tyler, I think it’s important for him to know that it’s been a solid year,” Bell said. “Nothing is going to change that. For his development, it would be great if he finishes strong. That’s important for all of us to finish strong, but he doesn’t have to do anything other than exactly what he’s done to this point [and] that’s pitch well and find ways to keep improving and developing.”