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The Gunners were eliminated from the Europa League by Sporting CP on Friday (AEDT), but they showed no sign of a hangover against managerless London rival Crystal Palace.
Gabriel Martinelli's 13th league goal of the season gave Arsenal the lead at Emirates Stadium and Saka, who set up that opener, added a second before half-time.
Granit Xhaka put the game out of the reach of Palace, who did pull one back through Jeffrey Schlupp, before Saka's second made certain of a sixth league win in a row.
Arsenal survived an early scare when Schlupp played in Wilfried Zaha, who cut onto his right foot and fired a low shot that hit the post in a lively start from Palace.
Joe Whitworth denied Saka at the other end, but the young keeper could not get a hand to Martinelli's impressive drilled shot across goal into the bottom-right corner.
Saka doubled Arsenal's lead shortly before half-time when exchanging passes with Ben White and coolly curling the ball away from Whitworth.
Palace was further behind 10 minutes into the second half through Xhaka's bundled finish after being played through by Leandro Trossard.
Schlupp's strike from six yards after Arsenal failed to deal with a corner gave the visiting fans something to cheer, but Saka's sharp first-time finish made certain of a routine win.