Georgetown’s Nate Lubick, left, and Otto Porter chase Alabama point guard Trevor Releford (9 points, six assists) up the court in the second half in Tuscaloosa. (Robert Sutton/AP)

The Georgetown men’s basketball team played its first true road game of the season on Thursday night, and what a task it was: A game in Coleman Coliseum against undefeated Alabama, ranked 12th in the country largely on the strength of its unforgiving defense.

So the Hoyas figured points would be at a premium and the outcome could come down to a late possession. Sure enough, junior forward Hollis Thompson had the ball in his hands with the game on the line, and after his three-pointer swished through the twine with 1.8 seconds left and Alabama’s desperation heave clanked off the rim, Georgetown celebrated a 57-55 triumph before a capacity crowd of 15,383.

The Hoyas beat their second ranked opponent this season, won their fourth straight and left Tuscaloosa as one of the more surprising teams in the country. Playing their parts, seniors Henry Sims and Jason Clark and Thompson have helped to stabilize 10 freshman and sophomores whose inexperience figured to be an issue this season.

“We’ve had a few tests here, a few battles,” said Georgetown Coach John Thompson III, whose team also beat then-No. 8 Memphis in overtime, 91-88, in the Maui Invitational on Nov. 23. “But to come in here and win against a team that’s so well-coached on their home court where they don’t lose, it’s a big, big victory for our group.”

Clark scored a game-high 22 points on 7-for-11 shooting, rebounding nicely from a seven-point performance on Monday. Sims added 13 points, three rebounds and three assists. Thompson finished with 12 points, eight rebounds and three assists with no turnovers in a rugged victory in which Georgetown’s zone defense limited Alabama to 0 for 9 from three-point range in the first half and 19 percent for the game.

The Hoyas (6-1) looked to have matters somewhat in hand with a nine-point lead with just under three minutes to play.

But Alabama came storming back behind senior forward JaMychal Green, who scored seven consecutive points before junior forward Tony Mitchell made 1 of 2 foul shots to cut the lead to 54-53 with 55 seconds to play.

Shortly after Sims missed a reverse layup, Alabama took a 55-54 lead with 12 seconds to play on two free throws by Trevor Releford. Georgetown called timeout to set up the final play in which Clark found Thompson open on the right top of the arc for the dramatic shot.

“Hollis knew it was going in when we came out of the timeout,” Thompson III said with a smile.

The play was designed for Clark to come off a screen from Sims, but Alabama (7-1), ranked fourth in the country in field goal percentage defense, made sure there was no clean look at the basket. Clark soon found Thompson open along the top right of the arc and delivered a strike, and one of Georgetown’s smoothest shooters squared up and connected on a jumper that silenced the Alabama’s first sellout since 2003.

A closing kick gave Georgetown a seven-point lead at halftime, but Alabama came out inspired immediately after, and the crowd got back into the proceedings when Mitchell (team-high 20 points, nine rebounds) elevated for a rebound and slammed two-handed in front of the student section.

Clark answered with a three-pointer, his third of the game, to bump the lead to 26-18, but the Crimson Tide scored the next seven in a row. The surge started with Green (13 points), a preseason all-SEC first-team choice, making 1 of 2 foul shots, and when Hoyas sophomore forward Nate Lubick lost control of a pass, Mitchell finished on the other end with another dunk that prompted Thompson III to call timeout.

Alabama, though, was just as determined out of the stoppage, getting two free throws from Releford and a second follow dunk off a rebound from Mitchell to trim the deficit to 26-25.

Sophomore point guard Markel Starks ended the drought for Georgetown with a diving layup through congestion in the lane, and Thompson drained a three-pointer with 16:25 left in the game to push the margin to 31-25. The Crimson Tide came right back, however, when Releford’s basket counted on a goaltending against Sims, and Mitchell got a left-handed floater to go with 14 minutes to play.

Mitchell collected Releford’s pass for a lob dunk moments later, and after Thompson’s driving layup, Tevor Lacey sank Alabama’s first three-pointer of the game to cut it to 35-34 with 11:33 to go. The Crimson Tide twice more got within a point and finally took the lead for the first time since early in the first half, 41-40, when Lacey connected on two foul shots, setting up the frenetic final minutes.

“We knew they were a tough team,” Clark said. “We knew they weren’t going to just roll over. We had to stick together. We told ourselves that we were going to stick together, run our offense, keep playing defense and just play it to the [end of] the clock.”