James appeared unfazed by a bruised bone and the right elbow strain that had caused consternation for Cleveland fans to score 21 of his points in the first quarter as the Cavaliers stormed to a 36-17 lead, which they extended to 65-43 by halftime.
Elsewhere, the Phoenix Suns moved to within one win of a Western Conference Finals appearance by beating the San Antonio Spurs 110-96 in Game Three thanks to unlikely match winner Goran Dragic.
In the East, the manner of the James-led Cavaliers victory, which gave them a 2-1 series lead ahead of Game Four in Boston on Sunday, could prove tough for the Celtics to recover from.
"Terrible loss... it was embarrassing," Celtics forward Paul Pierce said.
"When you come home and you got Game Three in your home building after taking care of business on the road, you gotta come with a better sense of urgency." The loss surpassed the Celtics' 27-point defeat by the Indiana Pacers five years ago in a first round playoff clash.
James was well supported by his Cavalier team mates with all five starters scoring in double figures, including 20 from Antawn Jamison.
"We had three days to sit and feel the pressure and then bounce back," James said of their 18-point defeat by Boston on Monday. "Rest helped me and we were able to have a complete game." The victory allowed the Cavaliers to regain home court advantage in the Eastern Conference semi-final.
"You knew he (James) was going to grab the ball and attack all game," Celtics coach Doc Rivers told reporters. "I think he's healthy enough with the elbow injury." Kevin Garnett, nursing a sore foot, led the Celtics in scoring with 19 points while Rajon Rondo added 18.
Back in the West, the Suns trailed throughout their game with the Spurs until Dragic's basket to open the fourth quarter gave them a one-point lead.
The two teams would exchange the lead four times over the next 90 seconds until the Suns seized ahead for good.
Dragic, who has averaged 6.5 points a game in the playoffs, scored 23 in the fourth quarter and 26 overall in just over 17 minutes of playing time to lead the Suns to a 3-0 series lead.
"Coach (Alvin Gentry) said: 'If you feel it, shoot it,'" Dragic said after shooting five-for-five from three-point range. "After that the rim was huge." The Suns can wrap up the series in Texas with victory in Game Four on Sunday.
