Under constant rain, bitter cold and layer-penetrating wind, taking care of the football became job No. 1.
Fuller-Williams lost two key fumbles, both in the red zone, which could have bloated Mastery's lead further.
Gratz' Jacon Snipes, a senior, caused and recovered the first. Rashad Hawkins, a sophomore, and Laquan Solomon, a junior, also recovered gaffs for Gratz.
"My teammates and coaches told me to keep my head up because they know how I get out there after a turnover," Fuller-Williams said. "Especially me giving up the ball. That's really not like me. So they influenced me to keep my head up."
Luckily for the 17-year-old from West Philly, his teammates - especially the defense - came through.
Troy Franklin, a 17-year-old senior from Mt. Airy, set up Mastery's only score with an interception during, of all things, a punt attempt.
Shyheed Brown, Gratz' senior running back, scored his team's touchdown three plays after taking the opening kickoff 73 yards to the Mastery 11. However, Brown, who is also the punter, got in trouble after fielding a low snap and threw a desperation pass that fell into the arms of Franklin.
"I don't know," said Franklin, a 5-10, 175-pound defensive end. "I just saw the ball in the air. That was my focus. Being on the d-line you don't get many interceptions so when I saw the ball, my thing was to just jump and get that ball."
Three plays later, Fuller-Williams plunged in from seven yards out.
Quinlin Lambert, a junior defensive lineman, recovered a fumble later in the first half for Mastery, and sophomore Cameron Willis added a pick.
The defensive play of the game however, belonged to 17-year-old senior cornerback Jalil Nichols.
After a fumbled exchange between Fuller-Williams and quarterback Donovan Crabbe, Gratz took over with 2:13 remaining in the game at its own 32.
Brown and QB Musa Al-Sulaimani helped move the ball into Mastery territory, but an errant throw with 1:13 remaining fell to Nichols, who dropped an earlier INT attempt.
"I saw the QB looking to my side," said Nichols, who lives on Erie Avenue.
Nichols said he spied top Gratz receiver Nydair Rouse and jumped in front with the previous missed pick on his mind.
"When I was over there [before] I dropped it, so I knew I needed to focus and try to catch that one," he said. "And I made the big play. This is a good way to end my senior year. The best way."
At the conclusion, both teams, part of the same Mastery family, posed for pictures under a spitting sky. Each team called out postgame awards.
Jermaine Norris, a 19-year-old senior for Mastery, took home game MVP honors for his squad. Norris was steady at safety and also played some Wildcat quarterback. He has been a team leader all season, and asked his squad to continue fighting after a disappointing 32-7 loss against Martin Luther King in the AAA Public Leaguel title.
"I love my team," Norris said. "We've been working hard ever since we lost in the championship. The team just wanted us to go out with a win."
Fellow senior Michael Byrd, a 5-7, 217-pound defensive tackle with long locks like the Pittsburgh Steelers Troy Polamalu, waited quietly in the rain as his teammates fielded questions. He saved the most poignant words for last.
"Coming up here from Germantown where I played my freshman year, I didn't have much confidence coming here," he said. "But, I had brothers here. I had more than just football players here. I had family. And I'll love them forever no matter where I go or who I play for in the future."
On Twitter: @AceCarterDN