CINCINNATI -- The Boston Red Sox have won 12 of their last 15 games but have struggled to distance themselves from the equally hot New York Yankees in the American League East standings.

On Friday night, the Red Sox overcame a first-inning grand slam by Scooter Gennett, rallied for an important win over the Cincinnati Reds and gained some ground on the Yankees.

Rafael Devers hit a three-run homer during a four-run fourth inning and Boston then held on for a 5-4 victory over the Reds in the opener of a three-game series at Great American Ball Park.

"Good come-from-behind win here tonight," Red Sox manager John Farrell said. "We knew coming into this series that their left-handed hitters could be explosive in this ballpark. It played true to form in the first inning. Then were able to put up a four-run inning ourselves."

Boston (89-64) now leads the Yankees by four games in the AL East. The Yankees lost 8-1 at Toronto on Friday night, reducing Boston's magic number to six to clinch the division. The Red Sox already have clinched a postseason berth.

"We've been in first place for a very long time," said left-hander David Price. "We don't care what the Yankees do. We just go play our game."

Right-hander Rick Porcello, the reigning AL Cy Young Award winner, started for Boston and had a rare rough outing on the road, after posting a 1.35 ERA in his previous three starts away from Fenway Park. On Friday, he gave up four earned runs -- all on Scooter Gennett's grand slam -- with three walks and three strikeouts.

The combination of Price, righty Addison Reed, and closer Craig Kimbrel maintained the one-run advantage for the final five innings.

Price (6-3) pitched 2 2/3 innings, allowing three hits with a walk and three strikeouts to earn the victory. Reed gave up one hit in 1 1/3 innings and Kimbrel allowed a single in the ninth inning for his 34th save of the season.

"I know Rick didn't want to come out of that game, and I fully respect that," Farrell said. "David was good for 40 to 50 pitches. I just felt that going with a left-hander in David against the meat of their order was the right move to make. When everyone is fresh down there and we have those pitchers to go to, it worked out well tonight."

Gennett hit a grand slam on the first pitch he saw from off Porcello in the first inning to put Cincinnati ahead 4-1

It was Gennett's fourth grand slam of the season to set a new Reds' single-season franchise record.

"Scooter's been a really good topic to talk about all season," Reds manager Bryan Price said. "That seems to be what Scooter does. Some people are extremely comfortable in that situation. He's played really big for us on offense this year."

Rookie Sal Romano (5-7) took the loss for Cincinnati (66-88), which lost its fourth straight game.

Romano, a Long Island, N.Y. native and long-time Yankees fan, was looking forward to facing the Red Sox. But, he didn't have his best outing, allowing five earned runs with four walks and Devers' three-run shot through four innings.

The Red Sox loaded the bases with no outs in the first inning, but managed only one run on Mitch Moreland's sacrifice fly.

"We had a big opportunity in the first and they find a way to minimize it to one run," Farrell said.

Cincinnati, however, cashed in on its bases-loaded chance in the bottom half of the frame when Gennett crushed Porcello's first pitch deep into the right-field seats for his 27th home run this season and fifth career grand slam.

Boston's 26-inning scoreless streak was over, but the Red Sox regained the lead against Romano when Devers clobbered his ninth home run of the season, a three-run shot in the fourth inning to put them ahead 5-4.

"All I was trying to do was make contact and drive those runs in," Devers said through an interpreter after hitting his first homer since Aug. 19. "I was just lucky enough to hit the ball out."

NOTES: Reds 2B Scooter Gennett is the only player in major league history to have a four-homer game and three or more grand slams in a season. ... Gennett joined Hall of Famer Lou Gehrig as the second player with a four-homer game and four grand slams in any season. ... Reds C Tucker Barnhart on Friday agreed to a four-year contract extension through 2021 reportedly worth $23 million. ... Reds CF Billy Hamilton and 3B Eugenio Suarez returned to the lineup. Hamilton had been on the disabled list with a fractured left thumb. Suarez missed three games for the birth of his daughter, Nicolle. ... Red Sox LF Andrew Benintendi is a native of Cincinnati. He had roughly 1,000 friends and family members at Friday's game.