The 35-year-old defenseman, who was playing in his 938th career game, entered the night with three goals in 53 games this season.
The Oilers are the first team in NHL history to have a defenseman score a hat trick in consecutive games, with Evan Bouchard doing so in a 6-5 overtime win against the Washington Capitals on Saturday.
Connor McDavid and Zach Hyman each had a goal and an assist, and Leon Draisaitl had four assists for the Oilers (27-19-8), who had lost two of three. Tristan Jarry made 36 saves.
Mikael Granlund scored three power-play goals, and Beckett Sennecke had two assists for the Ducks (28-22-3), who were coming off a 4-3 overtime win at the Calgary Flames on Sunday. Ville Husso made 25 saves.
Granlund put the Ducks ahead 1-0 with his first power-play goal at 3:24 of the first period. He took a pass from Chris Kreider in the left circle and roofed a shot over Jarry’s right shoulder.
Hyman tied it 1-1 with his own power-play goal at 17:14, tapping in a cross-crease pass from Ryan Nugent-Hopkins at the left post.
Alex Killorn scored 55 seconds into the second period to put the Ducks back in front 2-1. Ryan Poehling won a battle with Ekholm and Vasily Podkolzin for Killorn's dump-in behind the net before passing out front to the forward, who beat Jarry's blocker from the edge of the crease.
Husso would preserve the one-goal lead by denying McDavid on a penalty shot at 3:18, but the Oilers would pull away by getting four goals from their defensemen in a 3:49 span.
Spencer Stastney tied it 2-2 at 4:36 when his centering pass for Kasperi Kapanen deflected in off of the right skate of Ducks defenseman Olen Zellweger.
Ekholm gave Edmonton a 3-2 lead at 6:28. Skating in on a rush, Ekholm swept a pass from McDavid back to Hyman before continuing to the net for a give-and-go that he put through Husso’s five-hole.
Darnell Nurse pushed the lead to 4-2 at 7:34. Poehling tripped himself up at the offensive blue line, allowing Nurse to pick up the puck and carry it in on a 2-on-1 rush before beating Husso short side under his blocker from the left circle.
Ekholm then made it 5-2 at 8:25. Following another Ducks turnover in the neutral zone, Ekholm skated in on a 2-on-1 and lifted a shot over Husso's glove from the left circle.
Granlund cut it to 5-3 on a power play at 13:41. He received a spinning cross-ice pass from Sennecke in the right circle and beat Jarry short side under his glove.
Granlund completed the hat trick with his third power-play goal to get the Ducks to within 5-4 at 13:38 of the third period. He took another a cross-slot pass from Sennecke and scored with a shot from the bottom of the right circle that deflected in off the skate of Nurse.
It was his third NHL hat trick and his first since Dec. 29, 2017, with the Minnesota Wild.
McDavid scored into an empty net to make it 6-4 at 18:12, and Ekholm completed his hat trick by scoring another empty-net goal with 11 seconds remaining for the 7-4 final.
