He eventually got into form, just in time to perhaps doom the Knicks' playoff chances.
James scored 38 points and the Heat survived an NBA-record 22 3-point attempts from New York's J.R. Smith in a 102-91 victory that kept Miami atop the Eastern Conference standings.
''You do your job and you live with the results,'' James said. ''We lived with the result of J.R. making some of those bombs.''
Chris Bosh added 14 points and Ray Allen had 12 for the Heat (53-23), who are a full game ahead of Indiana (53-25) and two up in the loss column in the East race. The Pacers lost at home to Atlanta later Sunday night.
Smith was 11 for 28 from the floor, 10 for 22 from beyond the arc, and took 10 3s in the fourth quarter alone while Carmelo Anthony didn't attempt a single shot in the period.
The single-game mark was previously held by Damon Stoudemire, who hoisted 21 3s on April 15, 2005.
''It's not really been a goal of mine,'' Smith said. ''I saw the open 3 and tried to take them. I had to take advantage.''
Smith finished with 32 for the Knicks, who got 14 from Raymond Felton and 13 from Anthony on 4 for 17 shooting. Anthony has been bothered by a sore right shoulder, but played 44 minutes.
''Melo is still hurting,'' Knicks coach Mike Woodson said. ''I couldn't rest him again tonight. That second half, he was giving us what he's got.''
A bad day got worse for New York when the Hawks-Pacers game went final. The Knicks (33-45) are two games behind the Hawks in the race for the final playoff spot, three in the loss column. And New York has only four games left.
''Our fate is almost now in Atlanta's hands,'' Anthony said. ''It's tough. ... My fate is in somebody else's hands.''
The start suggested it would be a great day for the Knicks.
James had four turnovers in the opening minutes and New York - which had its best opening 2 1/2 minutes offensively in at least a decade, according to STATS LLC - held a 16-3 lead.
''Flummoxing,'' Heat coach Erik Spoelstra said. ''It was bizarre. Our turnovers were, no offense to the Knicks, absolutely unforced.''
It was still 16-3 when Felton was whistled for a second early foul, and everything changed. The Knicks missed six straight shots and the Heat scored nine straight points. James - who had one turnover in the final 3 1/2 quarters - settled down and things started going Miami's way.
''I wasn't awake yet,'' James said.
Miami got snippy with one another in plenty of huddles during the game, something that Spoelstra seemed to particularly relish.
''Verbally spitting at each other, I like it,'' Spoelstra said. ''That's what we need to get ready for the second season.''
Miami's lead was 15 with just under 9 minutes to go before the Knicks made it interesting. Iman Shumpert missed a wide-open 3 with 3:30 left that would have gotten New York within four. James answered a layup at the other end and after Smith made his ninth 3, Mario Chalmers answered with one of his own, making Miami's lead 97-88.
So Smith made another, giving the Knicks life. And Miami again answered, this time Bosh doing the long-range honors to restore the nine-point edge.
Miami played without Dwyane Wade (hamstring), Greg Oden (back) and Chris Andersen (back, knee). Amare Stoudemire scored 12 and Tyson Chandler finished with 10 points and 11 rebounds for New York.
James had four turnovers by the time Miami scored six points. But he settled in before the quarter was over, outmuscling Tim Hardaway Jr. for what became a three-point play. Hardaway tried to wrap James up on a break, but the four-time MVP kept going, scored and then flexed a biceps muscle to the roaring crowd.
''Trying to make a play,'' James said.
And after that sizzling 14-point beginning, New York needed more than 13 minutes to score its next 14 points. A 31-10 run helped the Heat take as much as an eight-point lead in the second quarter, before the Knicks went into halftime up 50-48.
Miami found some breathing room by scoring the final seven points of the third. James laid it in while getting fouled with 4.1 seconds left - and as ''M-V-P'' chants rained down he gave Miami its biggest lead to that point, making the free throw that put the Heat up 73-64 entering the fourth.
NOTES: Jeff Van Gundy worked the game for ABC, sitting three chairs away from former Heat coach Stan Van Gundy, working for ESPN Radio. ... Bosh had no rebounds in the first half, then seven in the third quarter. ... A fan clad in Knicks garb caught a T-shirt thrown into the stands by a Heat dancer during the fourth quarter. He threw it back onto the court. ... Hardaway Jr. is 2 for 22 in two games in Miami this season.