Abreu missed on two fastballs and was behind 0-2.
"I was trying to make contact but I was kind of late, and I made an adjustment and shortened my swing up a little bit," Abreu said. "I choked up and it happened so I'm very happy."
What happened was a line drive into left field that brought Francoeur home to break the 9-9 tie.
That made up for Abreu's failure in the 10th inning when, with two on and one out, he struck out against right-hander Vicente Padilla.
"It was a totally different at-bat, different pitcher. Padilla was throwing some pitches that I couldn't see very well. I was looking for one pitch and I didn't get it," Abreu said. "But I had a chance to redeem myself in that inning."
The Red Sox came within a couple feet of winning the game in their half of the 10th. With runners at first and third with one out against right-hander Kelvin Herrera, left-hander Francisley Bueno was summoned to face lefty Jacoby Ellsbury.
"I was trying to get a strikeout or get an infield ground ball and with the infield in, it would give us a chance," Bueno said.
Ellsbury grounded to Hosmer, the drawn-in first baseman, and he flipped to catcher Salvador Perez, who made a sweeping tag to retire the sliding Pedro Ciriaco.
"That was a nice play by Salvador. Luckily the throw wasn't at his chest. It was kind of down so he had to go down and catch it and put the tag right on him," Hosmer said. "I knew it was hit too soft to double up Ellsbury, so I thought that was the only chance we had right there."
That play gave Perez a big charge.
"When I made that play I said, 'OK, we have to win this game,'" Perez said.
They did because Bueno ended that inning with a strikeout and pitched a scoreless 11th. After Abreu's tie-breaking hit, Greg Holland worked a perfect 12th for his seventh save and Bueno was rewarded with his first big league victory, getting him the traditional beer shower in the clubhouse.
"I'm very excited, very happy because it was a total team effort," Bueno said via translator Brayan Pena. "The team came from behind and the guys from the bullpen held the score, and we got the victory."
Early on, there were stand-in standouts for the Red Sox.
Aaron Cook, replacing the traded Josh Beckett as the Red Sox starting pitcher, overcame a rocky start and worked six solid innings. Mauro Gomez, filling in for traded first baseman Adrian Gonzalez, pounded four hits and had three RBIs as the Red Sox built up a 9-3 lead in the fourth inning.
Many of the 37,103 fans were just settling in their seats when Cook, working on just three days' rest, gave up three runs in the first inning before getting an out. The big hit was Alex Gordon's two-run double off the Green Monster in left.
Royals starter Jeremy Guthrie, however, was hammered for seven runs.
"I wasn't sharp," Guthrie said. "I really didn't execute too many pitches. When I was down, I missed down; when I wasn't down, I was up middle."
He also was out of the game in the third inning. Everett Teaford gave up two more runs in the fourth.
Then Cook cruised through the sixth but when left-hander Andrew Miller took over in the seventh, the Royals were back in business. After two outs and a Hosmer single, they put together a six-run inning. Gordon had a two-run single, giving him four RBIs, and Mike Moustakas, breaking an 0-for-18 skid, drilled a two-run triple.
"I never felt that we were out of that game," manager Ned Yost said. "In this park, you can pick up runs in a hurry. ... When it was 7-3, I thought if we hold them there. Then it was 9-3 and we couldn't give up another run, and the bullpen did a phenomenal job from that point."
Louis Coleman, Aaron Crow, Tim Collins, Herrera, Bueno and Holland combined for 7 1/3 scoreless innings.
When the 4-hour 31-minute marathon ended, the Red Sox had that big trade behind them, Gonzalez had already whacked a home run for the Dodgers, and Boston fans were looking at a team that had lost 67 games, just two less than the Royals.
"Today was a crazy day but it's kind of the business part of it and we realize that things are going to happen throughout the season that we can't control," Cook said. "We came out today, we played really good baseball, we battled our butts off all night. We'll clean up, come back [Sunday] and try to do it all again."
The new era will have to wait.