With the game locked in a 2-2 tie, the Cubs imploded in the bottom of the eighth. A wild pitch by Pedro Strop allowed Marco Hernandez to race home with the go-ahead run. Two more runs scored on a throwing error by shortstop Addison Russell on a grounder by Dustin Pedroia.
Until then, the end result seemed to be hanging on every pitch.
"This was a highly billed series," said Red Sox manager John Farrell. "A competitive series certainly. It was a good series win for us that was needed, there's no question about it."
Hanley Ramirez unloaded for a two-run homer over the Green Monster against Kyle Hendricks in the bottom of the first. That was the only blemish for the Chicago right-hander, who allowed three hits and two runs over six innings while walking three and striking out six.
The Cubs tied in the seventh when a wild pitch by Joe Kelly, who walked two with one out, completely escaped the sight of catcher Christian Vazquez, and Jon Jay scored from second. The original call was out, but Cubs manager Joe Maddon immediately challenged, and a brief review led to the call being overturned.
"It's somewhat ironic that this game swung on wild pitches, both for them to tie it and us to go ahead," said Farrell. "Good to see us continue to build the inning in the eighth."
Despite the loss, the Cubs finished April with a winning record (13-11), although not as dominating as their 17-5 mark last year.
"We came out of the gates so hot last year," Hendricks said. "That was a special phenomenon. Usually this is more what you expect [in April], guys finding their ways into their roles. To be able to still win ballgames is a good sign. We're not clicking on all cylinders. Once that starts happening, getting in the middle of the year, everybody will start rolling."
Meanwhile, the Red Sox completed the month with a 13-11 mark. If both teams play up to their capabilities, Sunday might not be the last time they play this season.
"It'd be nice to eventually end up in the last seven games of the year between these two teams," said Maddon.
MOMENTS THAT MATTERED Hernandez hustle sparks winning rally: The Cubs' Koji Uehara took over in the eighth, and Hernandez hit a chopper to first baseman Anthony Rizzo. Rizzo flipped the ball to Uehara but Hernandez won the footrace, as umpire Jordan Baker called him safe. The Cubs challenged, but the call would stand and Hernandez had the single that sparked a game-winning rally.
"I got there as quick as I could," Uehara said. "The runner was just faster."
Said Maddon: "Not covering first base really opened that whole thing up for them. Koji is such a pro. I think he thought Rizzo was closer to the bag."
Hanley's encore blast: Fresh off belting the longest projected home run at Fenway Park in the Statcast™ era on Saturday, Ramirez was at it again with a tape-measure shot that went through the light stanchion above the Green Monster in the bottom of the first. Statcast™ had this one at an exit velocity of 112.4 mph and a projected distance of 440 feet. The shot Ramirez hit into a parking garage behind Fenway on Saturday had a projected distance of 469 feet.
"More than anything, he feels confident so when he sees pitches up in the strike zone, there's no hesitation, there's no thought to what his swing is doing," said Farrell. "He gets a pitch up from Hendricks and jumps all over it. So much like the first pitch from [John] Lackey yesterday, he jumps on the first pitch again today. He's seeing the ball well."
QUOTABLE "With everything that happened this month and being on the road a lot, I'll take what we did right now and get on back home and try to build upon it. There's not a negative to be found for me." -- Maddon, looking at how the Cubs did in the first month of the season
"It was fun. I felt like there were a lot more Cubs fans here than I would've expected. It was fun to listen to the fans go back and forth." -- Red Sox left fielder Andrew Benintendi, on the atmosphere of the weekend
SOUND SMART WITH YOUR FRIENDS The Cubs' bullpen entered the game with the best ERA in the National League, and one of the reasons has been the performance of Carl Edwards Jr., who struck out two in one inning. He finished April without giving up a run over 10 innings in 11 appearances.
WHAT'S NEXT Cubs:Brett Anderson will face the Phillies on Monday night to open a seven-game homestand at Wrigley Field. The lefty is coming off a win against the Pirates in which he gave up one earned run over six innings. First pitch is scheduled for 7:05 CT.
Red Sox:Rick Porcello opens a four-game series against the Orioles on Monday, with the first pitch scheduled for 7:10 p.m. ET. Porcello has pitched well in his last two starts, giving up just two earned runs over 13 2/3 innings, but he lost both outings. This is already the third series between the Sox and O's this season. Baltimore has taken three of the five games.