Allen hit a go-ahead home run in the seventh inning right after Porcello was struck, Corey Kluber tied for the major league lead with his 16th win and the Indians beat the Red Sox 5-4 Monday night.
"That was intense," Allen said. "You really weren't sure (if he was staying in) especially after a hit like that."
In a meeting of AL division leaders -- and a matchup of the last two Cy Young Award winners, it was 3-all into the seventh.
Porcello (15-6) retired the leadoff batter and walked the next hitter. Yan Gomes followed with a liner that hit Porcello near the stomach -- Porcello retrieved the ball near the mound, threw to second for a forceout and then slid to his knees, grabbing the spot where he was hit.
Porcello was checked on the mound, took a practice toss or two, and stayed in the game. Allen then sent a drive into the Indians' bullpen for his second home run of the season.
"I don't think the one that hit him had any effect on the next pitch. The first changeup was a good one," Boston manager Alex Cora said. "Then he threw another one and he hung it."
Porcello said after he caught his breath that he was fine. He was more bothered by what he threw after that.
"The pitch to Allen -- I'm not trying to take anything away from him -- but I think even I could have hit that one pretty hard," he said. "That was not a good pitch and it came at the worst possible time."
Xander Bogaerts had an early two-run single and an RBI single in the ninth for East-leading Boston.
The Red Sox had the first two runners on against closer Cody Allen in the ninth, and scored a run on Bogaerts' dribbler with two outs before Ian Kinsler flied out with two runners on base, leaving them with just their fifth loss in 22 games.
"That's what's called holding on for dear life," Indians manager Terry Francona said.
Allen posted his 25th save.
"You can breathe a sigh of relief after throwing 27 pitches and 20 of them were questionable and seven of them were good," he said.
Kluber, who won his second Cy Young Award last year, gave up three runs and nine hits, striking out six and walking one in 6 1/3 innings.
Porcello allowed five runs on three homers, fanning six and walking one over seven.
The game featured four top contenders for the AL MVP award: Boston outfielder Mookie Betts, who leads the majors in hitting (.342), and DH/outfielder J.D. Martinez, the majors' home run (38) and RBI leader (106), along with Cleveland third baseman Jose Ramirez (second in homers with 37) and shortstop Francisco Lindor.
Trailing 3-0, Cabrera homered into Boston's bullpen in the fifth and Brantley hit his drive into Cleveland's bullpen the next inning.
Bogaerts flicked a low-and-away pitch into right-center with two outs in the first for his single.
Andrew Benintendi's opposite-field RBI single made it 3-0 in the third.
Francona, who managed the Red Sox from 2004-11, talked about one of his favorite players, Boston 2B Dustin Pedroia, who has missed most of the season recovering from offseason left knee surgery.
"There's nobody like him and I don't imagine there will be," Francona said. "He willed himself to be the player he is, and his body is paying for it."
SHOW THAT LEATHER
The clubs combined for a half-dozen highlight defensive plays. The best two were: a long running grab by CF Allen off the bat of Kinsler and a diving catch by LF Benintendi, robbing Allen.
Members of both pitching staffs were tossing footballs around in opposite sides of the outfield about 3 1/2 hours before the start, with Boston's crew laughing and smiling as it ran fly patterns.
Indians: DH Edwin Encarnacion (disabled list since Aug. 12, right wrist contusion) took batting practice on the field.
Red Sox: Cora said lefty ace Chris Sale (went on DL Saturday, mild left shoulder inflammation) hasn't thrown yet. "We're shooting whenever he's ready," Cora said. "We're not going to push him." ... C Christian Vazquez (DL, fractured right pinkie) has been catching bullpens and hitting soft toss. Cora hopes he'll start taking BP later this week. He also was in CF catching pop ups from a machine before BP. ... 3B Rafael Devers (DL, strained left hamstring) did some light running on the field.
Indians: Rookie RHP Shane Bieber (6-2, 4.37 ERA) is scheduled to make his first career start against the Red Sox on Tuesday.
Red Sox: RHP Nathan Eovaldi (5-4, 3.62) is set to start. He's 2-0 with a 1.99 ERA in four starts with Boston since being acquired from Tampa Bay before the trade deadline.
Red Sox sweep away concerns -- at least for now
The defending champs put aside their dismal start -- and the building panic of their fans -- with three straight wins at first-place Tampa Bay.
Lindor blasts first homer of season
In just his second game of the season, Francisco Lindor rips a home run to left field.
Kemp gets injured running into wall
Matt Kemp suffers a chest contusion after running into a wall in the Reds' loss to the Padres.
Smoak nabbed after Laureano overthrow, but Jays sweep A's
The Oakland Athletics caught Justin Smoak early, ending a wild sequence that began with another eye-popping play by center fielder Ramon Laureano.
Francona learned a great deal from MJ in minors
Terry Francona explains how much he learned from Michael Jordan's competitive mindset while coaching him in the minor leagues.
Braves strike early with Donaldson homer
Josh Donaldson takes Shane Bieber deep with a solo home run in the first inning.