Five months ago in the same building, Posh Alexander was recognized by the Big East coaches as one of the top five players in the league.

It was a preseason honor, but also an acknowledgment of a strong first two years of his career at St. John’s.

Fast-forward to March, and very little had gone according to plan for Alexander and the Johnnies.

A team with NCAA Tournament expectations struggled through another disappointing season, and Alexander failed to perform up to the preseason hype.

“It was just doubts,” the junior point guard said. “I was playing bad, I wasn’t playing to my best ability and I was getting in my head.”

Lately, he has turned a corner, a trend that continued Wednesday afternoon. Alexander started fast and keyed eighth-seeded St. John’s commanding 76-63 victory over No. 9 Butler in the first round of the Big East Tournament at the Garden.

Alexander had 13 points, five rebounds and two assists, as St. John’s earned a quarterfinal meeting with No. 1 Marquette, five days after the Johnnies nearly toppled the sixth-ranked Golden Eagles in Milwaukee.

“I had talks with my family, and they reminded me, ‘just remember where you came from, how hard you worked for this opportunity,’ ” Alexander, a Brooklyn native, recalled. “I just thought about it and I started being in the gym a lot more, shooting the ball and getting my confidence [back]. It’s more just me having confidence again and these last couple of games show it.”

Over the past 10 games, Alexander is averaging 13.1 points, 4.7 assists and shooting 47.3 percent from the field.

He’s hit six 3-pointers in the last two contests, and has been making an impact at both ends of the floor. Wednesday, he helped St. John’s advance to Thursday.

It, of course, has been in this spot before.

Six of the previous seven years to be exact. St. John’s performs well on the first day of the Big East Tournament, putting together a strong performance, only to wilt the following day.

The Red Storm at least has given themselves one last chance to turn this year around by making a run in the conference tournament.

They haven’t reached the semifinals since 2000. They nearly got there last year. St. John’s (18-14) led eventual Big East Tournament champion Villanova by 17 points in the quarterfinals last March in a gut-wrenching one-point loss.

The Red Storm will get a chance to knock off the top seed again on Thursday.

“There’s always another opportunity, and this is the opportunity we have now,” Alexander said.

St. John’s was dominant for most of this opening-round win, building a 21-point lead early in the second half. It crushed overwhelmed Butler on the glass, 53-28, and outscored it in the paint, 40-28.

It held off a furious Butler run in the final minutes. Joel Soriano, the Big East’s Most Improved Player and this team’s MVP, had the game’s biggest basket.

His offensive rebound and follow ended a 20-9 Butler run that had sliced the lead to 10.

Alexander then found Dylan Addae-Wusu for a 3-pointer and the lead was never really in jeopardy the rest of the way.

Soriano led St. John’s with 19 points, 15 rebounds and two blocks, freshman AJ Storr had 15 points and Addae-Wusu notched 10 points, 10 rebounds and four assists.

Simas Lukosius scored 23 points for Butler (14-18).

St. John’s is a major underdog to get past Marquette, which has lost just once since Jan. 15. It has the Big East Player of the Year in Tyler Kolek and scored 96 points in each of its two victories over the Johnnies.

Both games, however, were competitive, decided by 13 points.

“We know what’s at stake and what we have to do,” Soriano said. “We have to play better defense. Both times they scored 96 points, so I think it was really us defensively.

“But if we play our brand of defense and we control our turnovers, I think we’ll come out with the win.”

Andre Curbelo announced on Twitter he won’t be able to return during the Big East Tournament due to a concussion he suffered in a recent practice. Rafael Pinzon (indefinite suspension) remained away from the team.