HOUSTON — No starting pitcher in baseball throws a sinker like Luis Castillo‘s. The ball starts on one side of the plate and ends up on the other, moving nearly a foot-and-a-half horizontally on average, an optical illusion of a pitch if executed correctly, which the 73rd of his American League Division Series start Thursday unquestionably was. The only problem: Yordan Alvarez, the beyond-talented Houston Astros slugger, stood at the plate ready to prove the pitch’s fallibility.

The sinker left Castillo’s hand at 98 mph, wound up 4 inches off the outside corner and landed 371 feet away — another day, another playoff game, another deficit-erasing, go-ahead home run by Alvarez, another victory for the Astros, this one 4-2 over the Seattle Mariners to give Houston a two-games-to-none lead in the best-of-5 ALDS.

By now, Alvarez’s bona fides need no burnishing: At 25 years old, he is one of the finest, if not the very best, left-handed hitters in the world. What he has done over the first two games of the series, however, is new to the annals of postseason baseball history. In Game 1, Alvarez hit a three-run walk-off home run in the ninth inning to bring the Astros back from behind. And in Game 2, they were trailing again, down 2-1, before Alvarez drove Castillo’s sinker onto Minute Maid Park’s short porch in left field sent the crowd of 41,774 into a tizzy, a win that leaves them just one win away from their sixth straight AL Championship Series.

Never before had a player hit more than one go-ahead homer in the sixth inning or later of a postseason game while trailing. Alvarez did it twice in two games.

“I just try to disconnect from everything when I go up there to the plate,” Alvarez said. “I just kind of try to go in there with a plan of attack and just go out there, try to visualize everything that might happen there and … yeah.”

Yeah is right. Yeah, the Mariners, for the second consecutive game, felt good about where they stood, with Castillo outdueling Astros starter Framber Valdez, who allowed a pair of fourth-inning runs on a Valdez fielding error and Dylan Moore RBI single. Seattle, in the postseason for the first time in two decades, hoped to return to T-Mobile Park for Game 3 on Saturday with a series split.

Instead, the inevitability that is Alvarez arrived in the sixth. Rookie Jeremy Peña, hitting in the No. 2 hole, stroked his second hit of the day with two outs. Castillo started Alvarez with a turbosinker. He fouled it off. He returned with another. Alvarez did not miss this one.

“If you’re good, I’m good, too,” Castillo said. “I came with the same plan of just getting him out and he was able to make contact with that ball. … I’m not intimidated by any lineup. When I go up on the mound, I go up there to compete.”

Houston’s bullpen stifled the compete from the Mariners’ lineup. With the bases loaded in the top of the sixth and the game primed to be broken open, Astros manager Dusty Baker pulled Valdez, the quality-start king, with the bases loaded. Reliever Hector Neris induced a groundout from Cal Raleigh, setting up Alvarez’s heroics.

He didn’t stop there, either. In the seventh, with two runners on, he snagged a line drive in left field from Eugenio Suarez that might have been out of his reach in past seasons, when he was primarily a designated hitter. When Alvarez strode toward the plate again in the eighth, Mariners manager Scott Servais had seemingly learned his lesson. He held up four fingers to signal for an intentional walk — his 10th this season — even though reliever Andrés Muñoz already had walked Peña. On the next pitch, cleanup hitter Alex Bregman laced a single into right to score Peña.

“Obviously he has done some damage against us in this series,” Servais said. “He’s hot right now. You’ve got to recognize that. I think you kind of game plan in how you want to go through their lineup and the guys you want to be careful with. When you’re throwing balls 3, 4 inches off the plate and he hits ’em like that, he’s in the zone, and he’s a super talented player, and he’s made us pay here the last couple days.”

The plaudits for Alvarez did not end there. He had a similarly prolific division series and AL Championship Series last season before disappearing in the World Series, going a homerless 2 for 20. The early success has returned. And Dusty Baker, the Astros’ manager, only hopes that they can grant Alvarez the sort of stage befitting of one of his nicknames.

“I call him Grande,” Astros manager Dusty Baker said. “He comes up big.”