CINCINNATI — On Opening Day, Red Sox manager Alex Cora said Major League Baseball introducing the ABS challenge system was going to be “interesting.”

He had no idea how interesting it would get in first series of the season.

ABS was the fuel behind Saturday’s 6-5 extra-inning loss going from bad to worse. The Red Sox ran out of challenges by the third inning and as a result, were felled by home-plate umpiring from CB Bucknor so egregious it led to an eruption by the usually-stoic Trevor Story, and subsequent ejection for the intervening Cora.

“He has one job to do, it’s call balls and strikes,” Cora said. “And it wasn’t his best day.”

More patient, the Reds waited until the bottom of the sixth to request a challenge, and proceeded to go a perfect 6 for 6.

Almost forgotten in the late- and extra-inning chaos was Sonny Gray’s difficult Red Sox debut hours earlier. Neither he nor Reds starter Brady Singer pitched into the fifth inning. Gray needed 35 pitches to get through a seven-batter, two-run first inning that included an odd fielder’s choice by the Red Sox starter. The Reds had already taken a 1-0 lead and had runners on the corners with one out when designated hitter Eugenio Suárez chopped a ball between home plate and the pitcher’s mound. Gray gloved the ball, but it squirted out of his glove as he attempted to apply the tag, and Matt McClain was safe at home.

“As soon as he hit it I knew it was going to be a weird one,” said Gray, who explained that the ball wasn’t secured in his glove in a way that would allow him to “shovel pass” it to catcher Carlos Narváez. “I never cleanly fielded the ball, is what it felt like. … Looking back, I could have slowed it down, fielded the ball and gave it up to Narvi completely. Just never felt like I got a clean grasp of the ball. Weird play.”

Story’s second-inning error added another run to Cincinnati’s lead, but the veteran shortstop answered back in the following inning, with the first Red Sox home run of the year.

Gray walked off the mound after four innings, charged with three earned runs and one unearned on six hits, one walk, and five strikeouts. He threw 80 pitches, 51 for strikes.

“He finished strong, to be honest with you,” Cora said. “We didn’t make two plays. The error by Trevor, and the fielder’s choice by (Gray).”

Boston’s two failed challenges first loomed large in the fourth, when they pulled within a run on three consecutive two-out singles and a wild pitch, only for Story to strike out looking on a pitch that ABS would have immediately overturned.

“From our end there were some calls that we didn’t agree, but we had no challenge, so we had to live with it until the 10th,” Cora said. “Two days ago we were very excited about the ABS, and today we’re not too happy about it. I mean, the system is the system. We’re not too happy with the way things went after that. But that’s on us, too.”

The dearth of ABS challenges reared its head again in the bottom of the sixth when Red Sox Rule 5 pick Ryan Watson entered for his MLB debut and the Reds had runners on first and second with two outs. Watson would’ve had an immediate inning-ending strikeout by his fourth pitch, but without the ability to challenge, he issued a bases-loading walk on the seventh pitch.

Up came the veteran slugger Suárez, who hit 49 home runs last year. Watson got two quick strikes, before the Reds DH fouled off his third pitch and took a ball. It was then that Watson threw a sinker, which Bucknor called Strike 3.

Suárez challenged successfully. Ball 2.

Watson threw a four-seamer. Strike 3. Suárez challenged again. Ball 3.

With the bases and count at max capacity, Watson threw his seventh pitch of the at-bat. Suárez grounded the sinker toward the middle of the infield, where second baseman Marcelo Mayer made a slick play to end the inning.

“It was a very up-and-down, emotional at-bat against Suárez there with the challenges and whatnot, but I felt like I was able to lock back in,” said Watson, whose parents, girlfriend and extended family were in the stands for his debut.

Working past a second pair of successful challenges by Reds right-fielder Will Benson, Watson pitched a scoreless seventh, and then a scoreless eighth. His composure in one of the most peculiar debuts imaginable impressed Cora and his teammates.

“He has two strikeouts and no strikeouts in that inning, right? And showed a lot,” Cora said of the first double overturn. “After that (inning) he was amazing, he was really good. … He saved us today.”

“If we’re being honest, he gave us a chance, right? He saved us,” Gray echoed. “That was impressive.”

Meanwhile, the challenge-less Red Sox could do nothing about several overturn-able pitches, and by the top of the eighth the situation reached a boiling point. Bucknor missed two clear balls in Mayer’s leadoff strikeout-looking. But it was Story’s checked-swing, deemed a swing by Bucknor, that results in an inning-ending strikeout to strand two runners, that led to the shortstop’s Vesuvian outburst.

“I think we have to save a little bit more (of) the challenge for later on,” Wilyer Abreu said. “We lost the challenge too early.”

The Boston bullpen counteracted the bats and Bucknor as best it could. After Greg Weissert gave up a leadoff home run to Elly De La Cruz in the fifth, Red Sox relievers combined for five scoreless innings to keep the game within reach.

“They kind of jumped me early, and overall I just don’t feel like I put us in a good position to win the game,” Gray said. “I was just proud to see how everyone continued to fight, and the bullpen did an incredible job. They gave us a chance.”

Two strikes away from defeat, Abreu turned a splitter from closer Emilio Pagán into a game-tying solo home run and created a bottom of the ninth for Red Sox closer Aroldis Chapman.

Reds players were already bursting out of the dugout to celebrate a walk-off home run when the ball Spencer Steer hit landed in Roman Anthony’s glove instead of the left-field stands.

Chapman sent the game to extras, where ABS rules dictate that a team without remaining challenges gets one per inning. But after jumping the gun early, the Red Sox didn’t take advantage late. They didn’t request a challenge in the 10th or 11th, nor were they able to score the automatic runner from second in either frame. They tallied eight hits and five walks, but struck out 15 times and went 2 for 14 with runners in scoring position and 11 men left on base.

“We have to be better,” Cora said. “We’ve been talking about putting the ball in play, and we didn’t do it.”

The Reds celebration that had begun prematurely against Chapman in the ninth restarted with Justin Slaten on the mound in the 11th. Cincinnati evened the series on a walk-off RBI single by Dane Myers.

The Red Sox and Reds will play for the Opening weekend series win Sunday at 1:40 p.m. ET.