Walker made a trio of key 3-pointers in the fourth quarter and finished with 29 points, Jaylen Brown added 25 points and 11 rebounds, and the Celtics beat the Dallas Mavericks 116-106 Monday night.
"I was just trying to be aggressive, trying to make the right plays," Walker said. "My shot felt good the whole night. I was just missing them. Then, in the fourth quarter, just naturally, the competitive nature just comes out and I try to do what I can do to put the ball in the basket."
Marcus Smart scored 17 points, Daniel Theis chipped in with 11 and Brad Wanamaker had 10 for Boston, which won its eighth straight game since a season-opening loss at Philadelphia.
Jayson Tatum shot 1 for 18 from the field and scored only five points for the Celtics.
Luka Doncic led the Mavericks (6-4) with 34 points, nine assists and six rebounds. Maxi Kleber had 15 points with eight boards.
Kristaps Porzingis scored just four points on 1-of-11 shooting for Dallas.
"Porzingis had a tough night. We're just going to flush it and move on," Mavericks coach Rick Carlisle said with a laugh. "You know, there's nights like this. You've just got to flush it and move forward."
Porzingis took a lot of blame for the loss.
"I had an off night tonight, and guys stepped up," he said. "Guys fought until the end, and we were right there. If I had a better game, the result could have been much different."
The Celtics released a statement during the opening quarter that said Hayward had surgery Monday to repair a fracture in his non-shooting hand. He was injured during their previous game in San Antonio when he collided with LaMarcus Aldridge as the Spurs' big man set a screen.
"I got word at halftime that surgery went well," Boston coach Brad Stevens said. "We're going to have to find other guys to step up, especially off the bench."
Boston trailed by two before going on an 11-2 spurt over a 1:32 stretch to move ahead 101-94 with 4:11 to play on Walker's 3 from the right wing. Smart then converted a three-point play.
Walker nailed his three big shots from beyond the arc in a span of 1:09.
Dallas took its first lead, 88-86, on Tim Hardaway Jr.'s one-handed runner in the lane. The Mavericks held a 92-90 edge before Walker took over.
The teams were tied at halftime before Boston opened the second half with a 15-3 surge. Smart started the run with a 3 from the right corner. Walker and Brown added 3s on consecutive possessions.
Doncic then started to take over, scoring nine of the Mavericks' 11 points as they closed to 84-79 at the end of the third quarter.
Mavericks: Porzingis didn't play in Dallas' previous game, resting as he returns from left knee surgery that sidelined him for the entire 2018-19 season. "He was (struggling), but you know this is what happens to great players," Doncic said. "They have a bad night. So expect, I think, the next game he's going to have at least 30 points. He keeps working. He just came back from injury."
Celtics: C Enes Kanter returned after missing seven games with a bruised left knee. "I felt it a little bit," he said when asked if he was fatigued during his nearly six minutes in the game. . Theis injured his right pinkie and went to the locker room early in the game. He came back to the bench and had the pinkie taped to his ring finger before going back in.
Boston jumped to an 8-0 lead and led by 10 twice - once in each quarter - during the opening half.
The Celtics honored 103-year-old Peter Fantasia, who served in World War II, on the court during a second-quarter timeout.
Mavericks: At the New York Knicks on Thursday in Porzingis' return to Madison Square Garden against his original team.
Celtics: Host the Washington Wizards on Wednesday.
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