Albion's challenge had stalled after collecting a solitary point from their previous four games.
But Hal Robson-Kanu, who was making his first Championship start since the opening day of the season, set them on the way to victory in the 51st minute before Matt Phillips doubled their advantage.
Harvey Barnes grabbed their third in the 82nd minute with substitute Dwight Gayle on target three minutes later with a cheeky back-heel.
Leeds, who had only lost once in seven games before facing Albion, would have gone back to the top of the table with a win but they were outplayed from the first whistle and all they had to show for their effort was a stoppage-time consolation from Pablo Hernandez, who headed in a pass from Samuel Saiz.
Albion started at a frantic pace and Robson-Kanu was inches away from giving them a ninth-minute lead when he sent a curling drive narrowly over the crossbar.
Tosin Adarabioyo then flashed a 13th-minute volley just wide after Craig Dawson had headed back a corner and 60 seconds later Jay Rodriguez forced goalkeeper Bailey Peacock-Farrell into a save after he lashed in a drive following a through ball from Barnes.
When Kalvin Phillips lost possession in the midfield after 22 minutes, Barnes led a swift counter-attack and, after exchanging passes with Robson-Kanu, he drove his shot into the side-netting.
Having managed to survive the Albion storm, Leeds had an excellent chance to take the lead but Hernandez blazed over from 14 yards after being picked out by Gjanni Alioski.
It proved only a brief respite for Leeds and United had the woodwork to thank for keeping them on level terms after 28 minutes when Rodriguez curled his shot from 20 yards on to the bar.
Albion gained their deserved reward through Robson-Kanu - seconds after Leeds were left seething when their appeals for a penalty were rejected after Kemar Roofe looked to have been pushed over by Dawson.
The Baggies surged straight up field and Rodriguez fed Robson-Kanu who beat Peacock-Farrell with a low-cross shot that sneaked in at the far post.
Leeds then effectively handed Albion their second when Phillips took the ball off Mateusz Klich just inside the United half before advancing towards goal and letting fly from 25 yards with a low shot.
Albion gave the scoreline an even more emphatic look when Adarabioyo collected Peacock-Farrell's clearance and lifted the ball to Barnes, who made no mistake from close range.
Gayle completed the rout when he scored on the turn from six yards after the ball broke to him when Rodriguez's shot was deflected to him off Liam Cooper.
Hernandez's header at the death was nothing more than a consolation for Leeds.