Nowitzki and Williams capped season-high scoring efforts with the first 11 points in overtime. Williams made a tiebreaking 3-pointer before Nowitzki scored eight straight points.
The Mavericks’ victory moved them within a half-game of the Trail Blazers for the sixth playoff position in the Western Conference. Dallas has 12 games to play, and Portland 11.
The Mavericks (35-35) also gained a tiebreaker by winning the first two of three games in the season series against the Trail Blazers (36-35). The teams play again in Portland on Wednesday.
Damian Lillard‘s layup tied it at 113 for Portland with 30 seconds remaining in the fourth quarter. Dallas’ Salah Mejri missed two free throws, and Lillard missed a 3-point attempt before time expired.
Nowitzki’s 20th career 40-point game was his first since Jan. 11, 2014. He has scored 20 or more points in eight straight games.
Williams’ previous season high was 30 points on Dec. 1 at Portland.
Nowitzki scored Dallas’ final six points of the second quarter for a 58-55 halftime lead. He led the Mavericks with 16 first-half points.
Lillard had 17 points and Plumlee had 11 rebounds for Portland in the half.
Matthews made three of the Mavericks’ five 3-pointers in the third quarter for a 90-82 lead.
Trail Blazers: In the first quarter, Portland made 14 of 23 field goal attempts (61 percent), including 6 of 12 3-pointers. In the second, the Blazers shot 5 for 23 (22 percent).
Mavericks: Chandler Parsons (sore right hamstring) missed the game. … Nowitzki played his 1,329th NBA game, moving into a tie for 13th place with Moses Malone.
Trail Blazers: Host Dallas on Wednesday.
Mavericks: Play at Portland on Wednesday.