Jason Chimera scored the solitary goal in the first period and Holtby???s 21 saves ensured that Washington took their 14th win in 19 games.
During his starting streak, Holtby has racked up a 14-2-4 record and has not allowed more than one goal in his last three games.
Philadelphia???s goalie Rob Zepp also produced a miserly display with 25 saves, including a terrific left-pad stop on Eric Fehr in the second period, but could not prevent the Flyers from slipping to defeat.
Elsewhere, Montreal Canadiens battled back for a 3-2 win over Columbus Blue Jackets after Max Pacioretty scored two power-play goals.
Pacioretty netted twice and PK Subban added another during a frantic third period, while Carey Price made 14 saves for the Canadiens, who have earned points in eight of nine games.
Kevin Connauton had opened the scoring for Columbus with his first shot of the game and Ryan Johansen doubled their tally in the third period.