BALTIMORE — Chris Sale was at his very best — right down to his momentous last pitch — in another meaningful victory for the Boston Red Sox.

Sale struck out 13 to become the first AL pitcher in 18 years to reach the 300 mark, and Boston moved to the brink of clinching a playoff berth by beating the Baltimore Orioles 9-0 on Wednesday night.

Sale (17-7) reached the milestone on his 111th and final pitch, a called third strike against Ryan Flaherty to end the eighth inning. The last AL pitcher to fan 300 batters in a season was Boston’s Pedro Martinez in 1999, when he set a club record with 313.

Red Sox manager John Farrell sent Sale back out for the eighth inning to give him a shot at getting No. 300.

Thing is, the left-hander had no idea he was at 299 when the inning started.

“No, I didn’t,” Sale said. “I went out there and struck out the last guy and everyone started losing it. I knew I was close, but I didn’t know I needed just one more.”

Mookie Betts and Deven Marrero homered for the Red Sox, who reduced their magic number for reaching the postseason to one. If the Angels lost to Cleveland later Wednesday night, Boston would be assured no worse than a wild-card spot in the AL playoffs.

The Red Sox, of course, would prefer to enter as AL East champions. They hold a three-game lead over the second-place Yankees with 10 games left.

“Given where we are in the standings and what is at stake, every win is important,” Farrell said. “Just getting into the playoffs is not our goal.”

After winning two straight 11-inning games over the skidding Orioles, Boston jumped to a 6-0 lead in the fifth and coasted to its 11th win in 14 games.

Betts and Marrero hit two-run homers in the fourth against Wade Miley (8-14) and Hanley Ramirez added a two-run double in the fifth.

Sale allowed four hits and walked none in matching his career high for wins.

“A dominant performance after a year that has been a dominant one,” Farrell said.

Sale reached double figures in strikeouts for the 18th time this season. He is the 14th pitcher in the so-called Live Ball Era (1920-present) to ring up 300 strikeouts in a season.

It was his 10th scoreless outing of the season, tying the team record held by Babe Ruth (1916) and Martinez (2000 and 2002).

“It was fun. I felt good tonight,” he said.

Sale faced a Baltimore lineup that was lacking two of its better hitters. Manny Machado was held out with an illness that manager Buck Showalter said the third baseman had been dealing with for nearly two weeks, and shortstop Tim Beckham was unavailable after having a wisdom tooth removed.

Not that it would have made much of a difference against Sale.

“He’s one of the best pitchers in the game and couple in the fact that we’re not really operating on all cylinders offensively, you end up with a shutout,” Showalter said.

In a streak that began in the sixth inning Monday night, Baltimore has gone 26 straight innings without scoring. The Orioles (73-80) were in the playoff hunt before losing 12 of their last 14 games.

SLUMP BUSTER

Boston’s Dustin Pedroia doubled in two runs in the eighth inning to snap an 0-for-18 skid. He missed Tuesday night’s game with a bruised nose.

PRICE CLOSING?

The Red Sox have plenty of pitchers in the bullpen, perhaps none more accomplished than former Cy Young Award winner David Price.

Price has been pitching in relief since returning from the DL on Sept. 14.

“He is available for multiple innings of relief tonight,” Farrell said before the game. “I wouldn’t be surprised if he were closing the game out.”

TRAINER’S ROOM

Red Sox: INF Eduardo Nunez (knee sprain) fielded grounders and did some running but still has a way to go before returning to the lineup. “While the hitting and fielding portion has improved, we find that the running portion is going to take longer than we first anticipated,” Farrell said.

Orioles: Closer Zach Britton will likely be shut down for the season. He’s going to get a stem-cell injection in his left knee, and it would probably be foolish to test him again in a season that’s gone south. “The most important thing for me is to be healthy going into next season,” he said.

UP NEXT

Red Sox: After a day off Thursday, Boston sends 17-game loser Rick Porcello to the mound in the opener of a three-game interleague series at Cincinnati.

Orioles: Gabriel Ynoa (1-2, 4.18 ERA) helps Baltimore launch a four-game series Thursday night against the Tampa Bay Rays, who — like the Orioles — remain only mathematically alive in the playoff chase.

Boston Red Sox starting pitcher Chris Sale throws to the Baltimore Orioles in the second inning in Baltimore on Wednesday, Sept. 20, 2017.