Arenas had 16 points in the 5-minute extra period, including 14 in a row for the Wizards during one stretch.
His scoring total was the most against the Lakers in 40 years.
Chamberlain, who played for the Warriors in Philadelphia and San Francisco and then for the 76ers before joining the Lakers, scored 60 or more points against them multiple times, the last a 65-point outing in 1966.
Arenas went 17-of-32 from the floor, including 5-of-12 from 3-point range. He made 21 of his 27 free throws and had eight assists and eight rebounds. Forty-three of his points came after halftime.
The previous franchise high was 56 by Earl Monroe on Feb. 13, 1968 -- also against the Lakers in overtime -- when the Wizards were the Baltimore Bullets.
"It was bound to happen," Arenas said. "I'm a scorer, so I was going to have one of those days where I was clicking. Most of the time when I've scored 46 in three quarters, we were blowing the other team out, so I didn't get to play in the fourth.
"But tonight was that time. It was a close game and I stayed in. I found the rhythm, especially in the fourth quarter and in overtime, and I never looked back."
Arenas' previous high was 47 points, against Miami last Dec. 30.
Asked how the Wizards' guard scored so many, Bryant said, "First of all, he shot 27 free throws. We as a team shot 30. Think about that."
Washington shot 60 free throws and made 47.
Bryant added, "Some of the shots he took tonight, you miss those, they're just terrible shots, just awful. You make them and they're unbelievable shots."
Lakers coach Phil Jackson said Arenas was spectacular.
"He made a lot of different shots, drives, 3-pointers, and still had that energy left to finish that game off," Jackson said.
Bryant, coming off a 53-point performance his previous game, went 15-of-24 from the floor and 8-of-10 from the line. He made 7-of-11 from beyond the arc, part of the Lakers' franchise-record 44 shots from 3-point range. They made 19, including 5-of-9 by Vladimir Radmanovic.
Bryant, who scored just four points in overtime, finished with 10 assists and eight rebounds.
Antawn Jamison had 25 points and 13 rebounds for Washington, and Caron Butler scored 27. Radmanovic, starting in place of the injured Lamar Odom, had 27 points, and Luke Walton had 15 points and a career-high 11 assists.
Washington led by as many as 17 early in the fourth quarter, but the Lakers came back to catch them at 126-all and send the game into overtime.
The victory was the Wizards' fourth in five games against the Lakers, but only their second in the last 14 meetings in Los Angeles. Washington also won for just the third time overall in 11 road games this season, and the Lakers lost at home for only the fourth time in 17 games.
Arenas had 12 points in the third quarter, including a 3 with 31 seconds left to put Washington ahead 90-80 to start the fourth period.
Washington was up 59-49 at halftime, with Jamison scoring 17 points and pulling down eight rebounds. Arenas also had 17 first-half points.
Bryant, who took only one shot in the first quarter and whose only points came on a pair of free throws, scored 16 in the second quarter.
Arenas scored 12 points on 6-of-9 shooting in the first quarter, Jamison had 10 points, and DeShawn Stevenson added four for all the Wizards' points in their 26-20 lead.
Radmanovic had 10 points to help Los Angeles stay close.
- Bryant had scored his season-high 53 points as Los Angeles came from 21 points down to beat Houston in double overtime on Friday.
- The Wizards' 11-point victory over Miami on Friday had put them at .500 for the first time since they won three of their first six this season.
- Washington was without C Etan Thomas, not on the trip because of a sprained left ankle. Los Angeles F Odom is out for at least a month with a sprained right knee.