OAKLAND -- As the Red Sox’s rotation has been reshaped by performance and injuries over the course of the season, Brayan Bello has emerged as a beacon of consistency.

With every ace-caliber performance, it's easy to forget that the 24-year-old is navigating his first full season in the Majors and, as such, is not immune to growing pains.

Bello allowed a trio of two-run homers as the Red Sox fell to the A's, 6-5, on Wednesday afternoon in the rubber game at the Coliseum. It was Boston’s first series loss since being swept at home by the Marlins from June 27-29.

"It's part of it, right? He's not going to be perfect," manager Alex Cora said of Bello. "Usually, they don't hit the ball out of the ballpark, [and] they did -- so let's get ready for the next one. Control wasn't great, the changeup wasn't good early on and obviously, they did a good job offensively."

Having tossed seven consecutive quality starts entering Wednesday -- the most by a Red Sox starter age 25 or younger since Eduardo Rodriguez in 2017 -- Bello took the mound in the bottom of the first with a two-run lead on Justin Turner’s 15th homer of the season, but a two-run blast by A's center fielder JJ Bleday evened the score.

Bello surrendered a pair of additional two-run blasts to right fielder Cody Thomas in the second inning and third baseman Jace Peterson in the fourth. It was the first time in Bello’s career that he yielded three home runs in a game.

"Nothing changes," Bello said in Spanish through interpreter Daveson Pérez. "Keep the same routine, keep the same mentality and just get ready for the next start."

In his past three starts, Bello has given up six home runs after permitting only seven through his first 13 outings of 2023.

The long balls hit by Bleday and Peterson both came off Bello's four-seamer. Entering the series finale, left-handed batters had been pounding that pitch, slugging .556 against it.

"We need to go up at some point during at-bats," Cora said. "You cannot live downstairs, you know, sinker, changeup. … The slider is developing. The cutter is what he's developing now, and it's a pitch that obviously he wants to use up in the zone to get chases."

Bello introduced a cutter earlier this season in an effort to offset the damage against his four-seamer, but the results have not been consistent.

"I need [the cutter] to be able to set up some of my other pitches," Bello said. "It's just a work in progress."

Though the Red Sox were able to rally within one run after a surge in the middle innings, they were unable to come back from Bello's uncharacteristic outing.

Following Tuesday night's shutout loss, Boston got off to a promising start by plating two in the first inning on Turner's homer off left-hander Ken Waldichuk. Turner has hit safely in 15 straight games, the longest active streak in the Majors and the second longest by a Red Sox player age 38 or older (Ted Williams, 17 games in 1957).

By the top of the sixth inning, the Red Sox had taken advantage of a sloppy A's defense that committed four errors by tacking on three more runs. Boston seemed poised to add on, but like the previous game, the Sox squandered opportunities by going 2-for-11 with runners in scoring position.

Down the stretch, Boston may look back at this entire three-game set as a missed opportunity of its own. On Tuesday night, the three leading teams in the American League Wild Card race -- the Rays, Blue Jays and Astros -- all lost, and a Red Sox win would have brought them within a half-game of the third spot.

Instead, Boston (51-46) dropped two of three games to the last-place A's (27-71). The consensus among the Sox is that they can't dwell on how they fell short and instead must flush the series and move forward.

The team has faith that Bello can do the same after Wednesday's tough outing.

"He's been fantastic for us," Turner said. "Pounding the zone, using all of his pitches. Unfortunately, today he just made a couple mistakes and those guys didn't miss it. But he'll be back out there … and I like our chances of winning anytime he's on the mound."