"If you go up and you block it, you're going to be on the highlight," Allen said. "You get dunked on, you're going to be on the highlight. So just go up and protect the rim.
That approach led to a remarkable block on James in the first quarter of the Nets' 115-110 win over the Los Angeles Lakers.
Allen met James above the rim in the second minute of the game, rejecting the attempt and putting himself on a short list of players to block one of James' dunk tries.
Allen is only the eighth player to block the four-time MVP, who has been denied just nine times in 1,850 dunk attempts in his career, according to ESPN Stats & Information.
"That's a helluva list to be on. He's an amazing player," said Allen, 20. "I got the chance to do it, so I'm on the list forever now."
James offered his assessment.
"He's in his 20s; I'm in my 30s," James said. "It takes me a little longer to get warmed up. But that's fine. I mean, you're a shot-blocker. You should, you can, get a block. It happens. It's probably all over social media, so that's cool."
Nets coach Kenny Atkinson said Allen's block was a catalyst in the Nets' win.
"I thought that got us going," Atkinson said. "I thought that got the crowd going.
"I thought he made a statement with that block."
The Nets (14-18) won their sixth straight game -- an NBA high this season -- thanks to Allen's rim protection, along with 22 points and a career-high 13 assists from ex-Laker D'Angelo Russelland a host of contributions from others.
Brooklyn's bench -- led by Spencer Dinwiddie (18 points, six assists) and Jared Dudley (13 points, five rebounds) -- outscored the Lakers' reserves 48-18.
"That's the only way you have a chance to beat this team, if everybody plays well," Atkinson said. "And I thought they did."
The Nets most recently won six consecutive games in 2015.
LeBron, Allen break down the big denial
After Jarrett Allen meets LeBron James to block him at the rim, LeBron and Allen react to it.
LeBron getting denied on dunks is a rarity.
Jarrett Allen's huge denial on LeBron James' dunk attempt reminds us that James has had only nine dunks blocked over his career.