Cook didn't undo his performance with a bad pitch, but instead with an errant throw that sailed into center field instead of serving as an inning-ending double play.
"Yeah, I feel awful," said Cook. "I let the team down. We're trying to win games, and that was a game we should have won. We lost because I made an error."
It only added to a period of intense frustration for the Red Sox, as they've gone 11-17 since star slugger David Ortiz went down with a right Achilles strain.
"You just pointed out the record. When he was here, when he was playing, he was our MVP," said first baseman Adrian Gonzalez. "When you take him out, it affects the whole team. He's a great player. We're just wishing he gets well just as much as everyone else is."
At 57-61, Boston is four games under .500 for the first time since May 13. The Red Sox didn't lose ground in the American League Wild Card standings, remaining 6 1/2 games behind the Tampa Bay Rays, who were the victims of a perfect game by Seattle's Felix Hernandez.
With 44 games left, there has never been more urgency for the Red Sox to get hot.
Frustration boiled over in the top of the eighth, as Gonzalez was ejected for arguing that Orioles reliever Pedro Strop quick-pitched him. Manager Bobby Valentine came out to defend his slugger, only to be ejected as well.
"I wasn't ready to hit. That's what I went back to tell [home-plate umpire] Mike [Everitt]. I wasn't ready to hit," Gonzalez said. "There needs to be a universal interpretation of it. It can't be up to each individual umpire's discretion. The rule needs to be stated better, because obviously I wasn't even set. I was just sitting there waiting for him to come set so I can get into my stance. We're trying to win games. I'm the leadoff hitter, down two runs, trying to get on base and that at-bat gets taken away from me."
Gonzalez grounded out to second on the pitch in question.
"It was an emergency swing," said Gonzalez. "It was like, 'Whoa, what happened?' I was shocked I even put it into play."
For the second straight night, the Orioles scored five runs in the sixth. And for the second straight night, the Red Sox never recovered.
After Hardy's single, Nate McLouth followed with an RBI single to right-center, scoring Nick Markakis, who started the rally with a one-out walk.
What Cook desperately needed from Adam Jones was a double-play ball that could end the inning. That's exactly what Cook got, as he snared the crisp grounder himself. But instead of starting a double play, Cook's throw to second wasn't even close, sailing into center field and allowing the tying run to score.
"It's a play I've made over 100 times," said Cook. "I just didn't get my feet set, tried to make a quick throw. I had plenty of time and just yanked it. It's just a bad throw, and it ended up costing us the game. Stuff like that, I can't let happen. I've got to be able to set my feet, take my time, make a good throw and we're out of that inning with one run and we're in here high-fiving right now."
But high-fives have become elusive for the Red Sox, who are 2-4 with four games left on this road trip, and 4-10 in August.
"You know, you get the ground ball, you've got to cash in there," Valentine said.
Matt Wieters followed the Cook misfire with an RBI double over the head of Carl Crawford in left, giving the Orioles their first lead at 3-2.
Just like that, Cook's performance was over, and Valentine went to Andrew Miller. The lanky lefty got a shallow grounder from Chris Davis that Dustin Pedroia fielded and fired home to nail Jones. Jarrod Saltalamacchia did a nice job hanging on to the ball as Jones plowed into him.
Playing matchups, Valentine went next to righty Junichi Tazawa, and he gave up a fly ball to left by Mark Reynolds that Crawford seemed to misjudge, as it soared over him for a two-run double. That capped the damage in a five-run frame, giving the Orioles a 5-2 lead.
"I don't know. I didn't catch it. I know that," said Crawford. "It was a tough catch in my mind. It just sailed over my head, man. I don't think I could have made that catch to be honest with you."
The Orioles did what winning teams do. They found a crack, and they capitalized.
"Once you get to the fifth, sixth inning with no hits, you've got to start pressing a little bit," said O's first baseman Mark Reynolds. "The fans know about it. Everybody knows about it. J.J. broke the ice, then [Cook] made the error, threw the ball into center field and that opened the floodgates for us."