It wasn’t the first time Georgetown’s offense stagnated this season. Nor was it the first time its star forward, Otto Porter Jr., struggled to score.

But on the worst possible occasion, on the biggest stage in college basketball, it proved one of those rare times that the Hoyas couldn’t get the defensive stops needed to slow a streaking opponent or, failing that, get bailed out by an offensive eruption from someone other than Porter.

As a result, Georgetown, the No. 2 seed in the NCAA tournament’s South Region, got manhandled by 15th-seeded Florida Gulf Coast, falling 78-68 on Friday night to a university that didn’t even exist when the current Hoyas were born.

It was a sadly familiar postseason refrain for Georgetown, which hasn’t made it out of the NCAA tournament’s opening weekend in six years, not since reaching the Final Four in 2007. The Hoyas have now fallen to a double-digit seed in four straight years, and in five consecutive NCAA tournament appearances overall.

“I wish I could,” Georgetown Coach John Thompson III said when asked if he could pinpoint a common thread in the string of postseason disappointments. “Trust me, more than anyone on this earth I’ve tried to analyze it, think about it, look at it, think about what we should do differently. And I don’t know.”

Making a name for itself at the Hoyas’ expense was little-known Florida Gulf Coast, whose own coach conceded this week that most Floridians couldn’t place the Fort Myers school on a map. Now, the Eagles are just the seventh No. 15 seed to win its first-round game since the tournament was expanded to 64 teams in 1985.

And FGCU did it in high-flying style, delivering rim-rattling dunks and raining three-pointers over a vaunted Georgetown defense that had held opponents, on average, to 55.7 points per game. Before an awestruck crowd, FGCU scored 54 against the Hoyas in the second half alone.

“When things aren’t going your way, it’s hard,” said Porter, the unanimous Big East player of the year who was held to 13 points on 5-of-17 shooting. “They got out in transition and started to run. It’s hard with a team that’s knocking down shots like that.”

The Eagles’ reward, in addition to overnight name recognition, is a date with No. 7 seed San Diego State, a 70-55 winner over No. 10 Oklahoma on Friday night.

Georgetown, meanwhile, once again heads home far earlier than anticipated.

After taking an 18-11 lead, the Hoyas went more than eight minutes in the first half without making a field goal. The Hoyas trailed 24-22 at the half, and they were soundly spanked in the second half, falling behind by 19 before mounting a rally that came far too late. By then, when a three-pointer by Markel Starks with 51 seconds remaining pulled Georgetown within four, the whole arena, it seemed, was on its feet and on the Eagles’ side, not interested in witnessing a Georgetown comeback.

FGCU’s improbable victory was a triumph for second-year Coach Andy Enfield, a Johns Hopkins graduate who holds the NCAA record for free throw shooting percentage (92.5), made a fortune on Wall Street and used the freedom that bought to pursue his dream of coaching basketball.

The Eagles were paced by Sherwood Brown’s 24 points, with Bernard Thompson adding 23.

Starks, who led Georgetown with 23, was terrific early, accounting for nine of the Hoyas’ points in a 14-11 lead.

A tip-in by Nate Lubick with 10 minutes 5 seconds remaining in the half put Georgetown ahead, 18-11. But the Hoyas went cold from there, failing to make a field goal over the next 8:27.

Porter, marked step for step by Brown, the Atlantic Sun player of the year, struggled to get his shot to fall. As Thompson gave him a brief rest, FGCU scored six unanswered points as the Hoyas missed an uncanny number of layups and tip-ins.

Porter, driving to the rim as the clock ticked down in the first half, lost control of the ball instead. With it, the Eagles took their 24-22 lead to the break. Apart from Starks, who managed nine points in the half, no Hoyas player scored more than four in the first 20 minutes.

The Eagles stayed loose, returning to the court with eight minutes left in the break to practice shooting and, in the case of Brown, wave at fans shouting encouragement. And they wasted no time punching the Hoyas in the mouth once play resumed. Brown drilled a three-pointer 11 seconds in. Off a Porter turnover, Chase Fieler dunked in transition, making it 29-22. And the rout was on, with the Eagles romping to a 15-2 run, playing with inspired abandon.

Florida Gulf Coast 78, Georgetown 68