MINNEAPOLIS -- Brayan Bello's fourth inning on Monday against the Twins appeared to show the next positive step in the talented rookie’s progression. 

The top-ranked pitching prospect and No. 3 overall prospect in Boston’s farm system per MLB Pipeline, Bello held Minnesota's offense in check for the first three frames, before loading the bases with no outs in the fourth. In previous starts, that type of situation had gone awry.

Instead, Bello came right back to force a pair of fly balls and a groundout to limit the damage to one run and maintain Boston’s slim lead. 

Then came the fifth inning. 

• Box score: Twins 4, Red Sox 2

Bello walked Luis Arraez on four pitches and Carlos Correa on six, his command abandoning him. That led to a quick hook from manager Alex Cora. Three batters later, a 2-1 lead had turned into a 4-2 deficit and eventual loss at Target Field, as Boston's shaky bullpen couldn’t strand those runners. 

"It’s tough. He needs to be more aggressive in the zone. ... He’s going to learn and keep moving forward," Cora said of Bello's performance.

It’s the conundrum the Red Sox face as they hope to make a late push for an AL Wild Card spot while simultaneously allowing Bello to work through his growing pains. They need Bello to improve, but don’t have the leash necessary to let him make many mistakes, especially not with the club now eight games back in the Wild Card race. 

"Everything starts with starting pitching and we need to get to the next level. Five [innings] is good for us, six is great, especially what we had, bullpen-wise," Cora said of the decision to give Bello the fifth. "We had to do it."

Bello had only completed five innings once before, in his previous start on Wednesday vs. the Blue Jays. It also happened to be the best start of his young career, as he allowed just two runs and one walk to Toronto's potent lineup.

It’s something Cora said needs to be a regularity, not a flash in the pan. But on Tuesday, Bello's 29-pitch fourth inning seemed to take its toll. He entered the fifth inning with 74 pitches, the most he’s had in a game since July 11. And from the first pitch of the fifth, his command was clearly gone. He walked Arraez on four pitches that didn’t sniff the zone and immediately fell into a 3-0 count against Correa, eventually missing low and inside to walk him on a full count. The inherited runners scoring on Gio Urshela's double resulted in Bello winding up tagged for three earned runs on five hits and three walks over those four-plus innings. He’s 0-4 with a 7.27 ERA in seven games (five starts).

"I was pretty upset because I was controlling the game," said Bello, who had moved through the first three innings quickly. "I was in the game and I was getting outs, and those two walks got me out of my game. I felt I was doing well and I was going along with the game real well, it just got me."

That forced Cora to go to the bullpen earlier than he wanted, replacing Bello with Matt Strahm, who retired Max Kepler on a groundout and struck out Kyle Garlick before walking Jose Miranda to load the bases. Looking to get out of the inning unscathed, Cora called on John Schreiber, the team’s best reliever by ERA who has been used almost exclusively in late-inning situations. That decision backfired as Schreiber immediately gave up the game-changing hit to Urshela, and has now allowed 11 of his 23 inherited runners to score since July 14.

"We were just trying to get to the sixth," said Cora, who was frustrated postgame, but not discouraged. Bello is "learning a lot" and "will be OK," he said. 

He has reason for optimism. Bello has steadily improved, allowing four or more runs in each of his first three starts but three or fewer in the three since.

"I’m learning a ton. Every time I go out there, it’s more information," Bello said. "I’m going to go back and look at the game, look at the video in that specific situation, probably look at it with the pitching guys and see what differences and what adjustments I can make for next time."

Short term, it may provide some hiccups. Long term, Cora has no doubts about the rookie.

"The stuff is really good," he said.