Martinelli opened the scoring the 28th minute after turning in Saka’s cross.
Saka added a second in the 43rd after collecting a pass from Ben White and finishing low past Palace goalkeeper Joe Whitworth.
Saka then saw an effort cleared off the line as Arsenal started the second half in the same dominant manner as it ended the first.
Xhaka made it 3-0 in the 55th after exchanging passes with Leandro Trossard and finishing from close range.
Schlupp pulled one back for Palace in the 63rd, but any thoughts of an unlikely comeback were ended when Saka struck again in the 74th.
Palace is three points above the relegation zone, but fellow strugglers Bournemouth, West Ham, Leicester, Nottingham Forest and Leeds have games in hand.