By the fourth quarter of Wednesday’s game against Magruder, just about every ounce of strength had been sucked from Aaron King’s lower body. His hamstrings, calves, toes — everything was cramping up as the Gaithersburg senior point guard laid on his back at midcourt while the action raced around him.

Most of King’s energy had been poured into Gaithersburg’s newly minted 1-3-1 half-court trap, a defense that elevated the tempo for the run-and-gun Trojans and forced a slew of Magruder turnovers in Gaithersburg’s 70-65 win at home. With the victory, the Trojans advance to Thursday’s Maryland 4A West region semifinal against Clarksburg.

The Trojans (21-2) entered Wednesday’s game amped up for revenge after falling to Magruder in January. Along with pushing the pace offensively, Gaithersburg quickly employed a 1-3-1 trap that left the Colonels out of sorts and unable to get leading scorer Joe Hugley going in the post. An Anthony Tarke dunk in transition punctuated a first quarter that saw every Trojan starter score as they built a 25-16 lead.

“We thought Magruder might try to switch things up offensively, so after playing man-to-man against them last time, we showed our 1-3-1 defense for the first time and I don’t think they were expecting it,” said Tarke, who finished with a team-high 21 points. “We had two or three days of intense practices getting ready for it and it helped shake things up.”

Though turnovers continued to hamper them, the Colonels (16-8) managed to slow the tempo and pull within four points at the start of the second half. But when Hugley (21 points) went to the bench with his fourth foul, Magruder’s offense stalled, and they went scoreless for the final five minutes of the third quarter.

Meanwhile, the Trojans built a 13-3 run on transition buckets and frequent trips to the foul line.

“Our big goal was to get big Joe in foul trouble,” said Geron Braithwaite, who finished with 12 points. “We knew they’d struggle if they didn’t have him in there.”

But the Trojans’ struggles from the free-throw line, where they shot just 15-of-22 in the second half, left the door open for Magruder. With Hugley back in the lineup and Magruder employing its own full-court trap, Gaithersburg’s lead shrunk to 66-60 with 35 seconds to play.

Out of a timeout, the Trojans reverted back to their up-tempo style, as Braithwaite caught a long pass in transition and scored the easy layup to seal Gaithersburg’s ninth straight win.

“We couldn’t really get our offense going in the second half,” Tarke said. “But we know offense wins games and defense wins championships, so we relied on that.”