James, who is out with knee and back soreness, missed his fourth in a row and fifth of the season. The Cavaliers are 1-4 when the four-time MVP doesn't play and have dropped 5 of 7 overall.
Nowitzki has 27,397 career points and is 12 shy of tying Moses Malone for seventh place all-time.
Kevin Love scored a season-high 30 points, but the Cavaliers couldn't stay with the Mavericks (25-10), who had five players in double figures.
Kyrie Irving left in the third quarter with lower back tightness and didn't return. He was 2 of 9 from the field and scored a season-low six points.