Now he's an NBA Finals record-holder, and a big reason why the MVP's chances of a second consecutive championship are in serious trouble.
Setting a Finals mark with 25 3-pointers, Green finished with 24 points and went 6 of 10 from long range in Game 5 against the Miami Heat, helping lead the San Antonio Spurs to a 114-104 victory Sunday night.
Deemed too raw and unpolished to remain on the roster with James and Cleveland three years ago, Green is the most prolific 3-point shooter on the NBA's biggest stage.
"It seems everything is going right for me. I feel truly blessed," Green said. "The basketball gods are in our favour right now."
Green is 25 for 38 from long range in the Finals — 66 per cent — having hit at least four 3-pointers in every game against Miami except one.
Green set the mark playing against Heat guard Ray Allen, who set the record when he hit 22 3-pointers while helping Boston win its most recent title in 2008.
Yet even Allen — the NBA's all-time leader in 3-pointers — didn't shoot with this kind of precision in the Finals. Allen, who has 11 3s against the Spurs, shot 52 per cent in that six-game win against the Los Angeles Lakers.
"It's an honour to be even playing on the same floor as some of these guys. Growing up, I watched him play all the time," Green said of Allen. "To think I broke a record of his is surreal."
Green still has at least one game left to add to his total, starting with Game 6 on Tuesday night in Miami.
Spurs forward Tim Duncan said he hopes Green doesn't cool off anytime soon.
"He's been unbelievable. Especially on this stage," Duncan said. "He's been shooting the ball so well. We're asking him to defend Dwyane Wade and LeBron and all these guys. He's got a lot on his shoulders and he's stepped up and answered the bell."
The Spurs are one win away from hoisting a fifth championship in the Duncan era.
But Duncan has never leaned on a role player so heavily like this in the Finals. Although the Spurs won their first titles with the help of a revolving cast of big-shot players — Sean Elliott, Robert Horry, Steve Kerr — none carried the scoring load like Green.
Green has emerged as the unlikely leading scorer for the Spurs this series, averaging 18 points. That's nearly eight more than his season average, and his 90 points in these five games are more than what Green scored in his first two NBA seasons combined.
Not bad for a player coach Gregg Popovich cut twice before Green finally won him over last season.
"When you do it for 82 games, the only thing left is to see if you can do it when the real lights come on in playoff time," Popovich said. "He's pretty much answered that question."
The Heat have yet to find an answer for Green. Miami guard Dwyane Wade, who has guarded Green this series, said he couldn't remember many players who shot the ball this well in the Finals.
He said Miami must do a better job back home of defending Green.
James said Green is making the most of his opportunities.
"He's trying to seize the moment," James said. "And he's doing great for his team so far."
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