By William Schomberg
Chelsea, who will face city rivals Arsenal in the Aug. 1 showpiece, had lost to United three times this season but looked brighter from the start at Wembley and took control with goals either side of halftime from Olivier Giroud and Mason Mount.
United were forced into a change at 0-0 late in the first half when Eric Bailly was carried off after clashing heads with fellow defender Maguire. United manager Ole Gunnar Solskjaer brought on Anthony Martial to create more attacking threat.
But it was Chelsea who took the lead 11 minutes into first-half stoppage time when Giroud flicked a cross by Cesar Azpilicueta at De Gea who failed to get enough of a hand on the ball to stop it spinning over the line.
Chelsea doubled the lead a minute after the restart when Mason Mount pounced on a poor pass by Brandon Williams to shoot from the edge of the box. It looked like De Gea would make a comfortable save but he could only steer the ball into the net.
United struggled to create any chances to narrow the deficit and Chelsea sealed the win when Maguire, under pressure from Antonio Rudiger, connected with a cross from Marcos Alonso with his studs and diverted the ball past the hapless De Gea.
United scored a consolation goal when Bruno Fernandes converted a penalty in the 85th minute. (Reporting by William Schomberg; Editing by Ken Ferris)