The Cadets pull the upset on the top-ranked Panthers’ home court, 71-68, with a game-winning, last-second three-pointer. (Andrew Kloc for Synthesis/Koubaroulis LLC./The Washington Post)

No one within the crowded Paul VI gym knew how the final possession by St. John’s would play out Thursday night. Up to that point in the clash of WCAC boys’ basketball powers, neither team had been willing to relinquish control, leaving the score tied as the final seconds began to tick down.

“We ran motion and I was ready for whatever,” St. John’s guard Darian Anderson said.

The pass from a double-teamed Tre Campbell, the shot fake that shed the defender flying toward him and the open three-pointer that resulted — Anderson was ready for it all, draining the winner as the buzzer sounded to lift No. 2 St. John’s to a 71-68 win against No. 1 Paul VI in Fairfax.

Though the result proved much more dramatic than the teams’ first meeting this season, when Paul VI ran away with a 20-point win at St. John’s, Thursday’s outcome stung just as much for the losing team.

The Panthers (17-4, 9-2 in WCAC) had built a six-point lead with nine minutes remaining and were again using their size to outmuscle the Cadets (17-1, 7-1) on the boards. But St. John’s scrappy defense helped turn away Paul VI’s second and third opportunities at the rim, setting up transition baskets that pushed them back into contention.

“In the first half, we weren’t defending as well,” said St. John’s senior James Palmer, who finished with 14 points. “We had to come out and clamp down on defense a lot better in the second half, and we did that.”

When Mike Morsell (team-high 21 points) streaked in for a lay-up to put St. John’s up 58-57 midway through the fourth quarter, it marked just the fifth lead for the Cadets.

Marcus Derrickson, who had missed the past two games with a foot injury, and Evan Taylor (team-high 19 points) willed the Panthers back in control with a big three-pointer and several mid-range jumpers, respectively.

But after Palmer converted a three-point play on a pull-up jumper with 40 seconds left and Taylor followed with two free throws to tie things at 68, the stage was set.

For most of the night, Paul VI had disturbed St. John’s pick-and-roll plays with different defensive looks, sometimes switching defenders while other times double-teaming the ball. Knowing the final play could be defended several ways, Cadets Coach Sean McAloon called for his players to react, then attack.

Once a second Paul VI player charged at a dribbling Campbell, the senior swung the ball to Anderson, whose scoreless second half came to a dramatic end, sealing the Cadets’ third win against a ranked opponent in the past week.

“Big shots like that don’t come often, so I just took it,” said Anderson, who finished with 14 points. “These have all been big wins but we still can’t take anyone for granted.”