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.
Angels set to welcome injury-riddled Yankees
The New York Yankees will begin a four-game series in Anaheim on Monday against the Los Angeles Angels, but one would be hard-pressed to call them the Bronx "Bombers."
Peacock gets nod for Astros at home vs. Twins
Houston Astros manager A.J. Hinch is forever adamant about stressing the significance of quality at-bats and remains an ardent supporter of his team's ability to compile them no matter the circumstance and against any opposing pitcher.
Rockies look to stay hot against Nationals
The Colorado Rockies will try to continue being rude hosts to the National League East when they open a three-game series against the Washington Nationals on Monday night.
Minor looks to stay hot as Rangers visit A's
Two pitchers with a lot of promise but uncertain futures go head-to-head Monday night when the visiting Texas Rangers open a three-game series against the Oakland Athletics.
Sale seeks first win as surging Red Sox host Tigers
Fresh off a sweep of the first-place Tampa Bay Rays, the Boston Red Sox finally seem as if they're close to putting their woeful start to the season behind them.
Phillies turn to red-hot Arrieta against Mets
The Philadelphia Phillies will hand the ball to their hottest starting pitcher when they visit the New York Mets on Monday night.