The Lakers built a 19-point lead in the first half before blowing most of it in a disappointing third quarter, but they held strong in the last as Davis racked up 14 points and seven rebounds.
Josh Jackson made a season-high 20 points for the Grizzlies.
In Orlando, Luka Doncic accumulated 33 points, 10 rebounds and eight assists to guide the Dallas Mavericks to a 122-106 win over the Magic.
The Mavs were also well served by Maxi Kleber, who managed a career-high 26 points to help his side improve to 19-8 on the road.
The Pelicans, who led by as many as 22 points, have now won four of their past five games to draw closer to the playoff spots, in 11th place in the Western Conference.
Williamson, a No. 1 draft pick, was playing just his 11th game after a right knee injury sidelined him for the first half of the season.
CJ McCollum had 27 points and 10 assists in Portland's third consecutive loss.
In other games, the Toronto Raptors won 118-101 at home to the Phoenix Suns, the Boston Celtics won 127-117 at the Minnesota Timberwolves, the Oklahoma City Thunder beat the visiting Denver Nuggets 113-101, the Cleveland Cavaliers won 113-108 at the Washington Wizards, the San Antonio Spurs triumphed 113-104 at the Utah Jazz, and the Indiana Pacers were 106-98 winners at the New York Knicks.