Arsenal manager Mikel Arteta knew victory would see his team overtake Manchester City at the top of the table and the result never looked in doubt from as early as the fifth minute when Gabriel Martinelli opened the scoring.
Saka’s replacement Reiss Nelson scored a brace to go with goals from Gabriel Martinelli, Thomas Partey and Martin Odegaard. Even so, the injury to the winger will be a major concern for manager Mikel Arteta and his England counterpart Gareth Southgate three weeks ahead of the start of the World Cup in Qatar.
Arsenal move to 31 points from their 12 games, two ahead of Manchester City, while an outclassed Forest remain rooted to the bottom of the table with nine points having played a game more.
Meanwhile, the game was a dose of reality for Forest, which had beaten Liverpool last week.
It started with Martinelli putting Arsenal ahead when stooping to head in a Saka cross.
Saka hobbled off shortly before the half-hour mark after trying to run off an earlier knock.
He was replaced by Nelson, who had a decisive impact, taking centre-stage on his first Premier League appearance since the opening-day defeat at Brentford last season.
He doubled the lead with a finish high into Dean Henderson´s net in the 49th-minute after the England goalkeeper had done well to keep out Nelson´s initial effort.
The points were secured just three minutes later. Nelson scored again as he turned home Gabriel Jesus´ cross before laying a pass into the path of Partey, who finished superbly from outside the box to make it four in the 57th-minute.
Odegaard latched onto a Jesus pass to score the fifth after 78 minutes.