The start was so promising, the latest example that when playing its best, Georgetown can compete with the top college basketball teams in the country. But the way it ended had Coach John Thompson III shaking his head in relief, a smile on his face as he conceded “a lot of things fell into place” Saturday at Verizon Center.

Despite being held without a field goal over the final 3 minutes 38 seconds of regulation, Georgetown upset No. 5 Louisville, 53-51, to improve to 4-1 since forward Greg Whittington, the team’s second-leading scorer and rebounder, was ruled academically ineligible earlier this month.

But even though a new potential sidekick for star forward Otto Porter Jr. emerged, it was an unheralded player from deep within Thompson’s bench that provided the game-winning basket.

With the score tied at 50, Georgetown redshirt sophomore Aaron Bowen swooped in from along the baseline after a missed lay-in by guard D’Vauntes Smith-Rivera. Bowen then used his left hand to flick the ensuing rebound over his shoulder and into the basket for a spectacular reverse tip-in. It was Bowen’s only field goal of the afternoon.

Thompson said after the game that Bowen, who was averaging just 1.8 points and 6.8 minutes entering Saturday, had been close to several other offensive rebounds earlier. So Bowen told him during the previous stoppage in play, “I’m gonna get one, Coach.”

“As soon as we went in the locker room, I told him, ‘I’ve never seen anything like that,’ ” said point guard Markel Starks, who finished with 17 points. “But I tell him all the time he’s probably one of the most athletic people on this planet, and when the shot went up, he just came out of nowhere. He just tipped it. It was unbelievable.”

After Bowen’s heroics, though, the crowd of 17,474 had to sit through several excruciating moments. Louisville (16-4, 4-3 Big East) had six chances to avoid its third straight loss since rising to No. 1 in the AP rankings.

The nerve-wracking sequence reached its climax when Porter, who finished with 17 points and 12 rebounds, had two costly turnovers in a row. The first came when he stepped out of bounds while catching an inbounds pass, but Louisville guard Russ Smith missed a jumper on the other end with 34 seconds left.

On the rebound, though, two Cardinals defenders hounded Porter. Instead of calling a foul, the officials declared the play a jump ball and Louisville retained possession with 29.5 seconds remaining. Coach Rick Pitino then decided to hold for a final shot, and senior Peyton Siva’s jumper from just inside the three-point line caromed harmlessly off the rim.

It was a fitting conclusion considering Siva and Smith, two of the premier guards in the country this year, were held in check most of the day. Siva, who battled foul trouble, had zero points and two assists. Smith scored only 12, nearly seven points less than his season average.

Both were outplayed by Starks, who “hit big shots when we needed him,” Thompson said.

The former All-Met from Georgetown Prep scored six points during a crucial 10-2 run in the second half after Louisville regained the lead momentarily with consecutive three-pointers from George Mason transfer Luke Hancock (12 points).

The Hoyas (14-4, 4-3) started red-hot from the field, connecting on eight of their first 10 shots to open the game. Though Georgetown hit just 11 of its 39 field goal attempts the rest of the way, it limited Louisville to 34.8 percent shooting, preventing Pitino from setting up his patented full-court pressure at times.

“You don’t want to make it mano y mano, but at some point you’ve got to take pride in playing defense,” Starks said.

As it turned out, Georgetown’s defensive resolve to close out the game was even more impressive than at first glance. Television replays showed that, while the ball was in play, the Verizon Center clock had stopped running for approximately 24 seconds with 6:07 remaining in the second half. No one appeared to notice the malfunction.

With a marquee victory in hand, though, Thompson was content to relish the breaks his team did get.

“You’re not gonna see too many times where Peyton Siva has zero points,” he said. “We did a terrific job on him, but I think a lot of things just happened to bounce our way today.”