Washington finished with three power-play goals, two in a four-goal second period that gave the Capitals a 6-2 lead.
Ovechkin, Nicklas Backstrom and Alexander Semin sparked that second period. Ovechkin had both of his goals, and Backstrom (one goal, two assists) and Semin (three assists) did all their scoring in the period as the Capitals broke the game open.
Knuble opened the scoring at 2:36 of the first period when he jammed the rebound of Brian Pothier's shot past Chicago goalie Corey Crawford. The Washington newcomer then made it 2-0 with a power-play goal 4:52 into the game, firing a quick shot past Crawford after a pass from Ovechkin.
Backstrom made a perfect pass that Ovechkin easily tapped into the net 1:45 into the second period. Ovechkin scored a power-play goal 95 seconds later to make it 4-1. Semin made a slick pass that set up Ovechkin's shot from the left circle.
Backstrom added another extra-man goal later in the second period. Tyler Sloan scored the other Washington goal late in that period for a 6-2 lead.
Goalie Semyon Varlamov finished with 26 saves.
The Capitals improved to 3-1-0. Chicago fell to 0-2-1 and has scored only four goals in three games.