Goretti (13-5) charged to its fifth straight win, mainly riding the shoulders of 6-foot-6 Gene Johnson, who powered his way to a game-high 22 points along with nine rebounds. He scored eight points in the decisive fourth period, including six after Chambers' clutch trey.
"Coach gives me that certain kind of look, and I know he wants me to get more physical and take over the game," Johnson said.
Goretti, which trailed 32-24 at halftime, became far more physical in the second half.
The Bulldogs (6-5), playing their third game in four nights, held the advantage despite Andre Hornes scoring only one point in the first 16 minutes and Q'Monte Matheny going scoreless. Nate Sowers scored 10 to pick up the slack.
"Even without our big guys scoring we led by eight at halftime because we ran our offense and executed," said Martinsburg coach Dave Rogers. "We had a lot of balls they took from us, we took a lot of bad shots and they really won the game because they were so physical in the second half."
Martinsburg held a 37-26 lead early in the third period on a deuce by Hornes, his only goal of the game, and a 3 by Scottie Smith.
Goretti's Kevin Brashears got the Gaels back within striking distance with a trey from the right wing and a bucket on a drive in transition to slash the deficit to 41-38 with 4:29 left in the third and keep the Gaels breathing.
The move of the game came early in the fourth when Johnson gave Goretti a 46-44 lead with 5:30 to play when he faked, put on a dazzling drop step and went to the basket from out near the left elbow.
Sowers tied the battle 48-48 with 3:10 to play before Chambers connected and the Gaels scored the final eight points in the last 2:04.
"We had to get them back this time," said Johnson. "There was a lot of trash talking going on and it was physical, but this is the type of game that just makes you play tougher."
Robertson felt the Gaels won the game with their defensive effort and Johnson's play on offense along with the effort of guard Trevor Cobb.
"Two big reasons were we shut down their big guys and Gene's effort which was probably his best on defense," Robertson said. "Trevor was great. His best of the year and he ran the team."
Cobb scored six critical points but also had four assists and battled under the boards with the big guys to grab seven rebounds, four in the final quarter. Spierenburg had nine points and six rebounds as the teams battled evenly on the boards, 32-32.
Each team effectively handled the ball, Goretti guilty of only 10 turnovers and Martinsburg 12. Johnson hit 10 of 15 from the floor as the Gaels shot 22 of 54 while Martinsburg ended 20 of 55.
Sowers led Martinsburg with 12 points and Nick Benavides had 10, while Hornes, who had 24 against Goretti in the first meeting, had four and Matheny, who had 22, tallied five.