Wigan continued their revival by pulling off a shock 1-0 win at Sky Bet Championship leaders West Brom to boost their survival chances.
Wigan are now three points clear of the relegation zone in 19th place, while Albion are six points clear of third spot.
Wigan created the first chance when Morsy's shot following a corner was spilled by Johnstone, who then held the follow-up from Joe Williams.
West Brom responded by going desperately close through Pereira.
Rekeem Harper helped the ball on to leave the Brazilian playmaker in the clear – but his toe-poked shot was blocked by Marshall's legs.
In an open game, Wigan went close twice in quick succession, with both chances falling to Massey.
Moore's angled drive was blocked by Filip Krovinovic from Roberts' searching ball as the visitors pressed again.
Wigan created the first opening of the second half when Roberts dispossessed Krovinovic deep in the visitors' half.
The loose ball ran to Jamal Lowe, who was allowed to run some 50 yards before blazing high and wide.
There were penalty shouts at both ends, but referee Tony Harrington was unmoved.
Then Wigan though they should have had a spot-kick for handball against Conor Townsend.
Wigan continued to press and Roberts forced Johnstone to block at his near post after the forward let fly from point-blank range when Morsy put him in after a corner.
Krovinovic was a whisker away with a 25-yard drive but Wigan returned to the attack to take the lead.
From Michael Jacobs' corner; Moore missed his connection, Krovinovic's attempted clearance looped up in the air, Cedric Kipre's hooked effort was blocked and Morsy rammed the loose ball into the top corner from 10 yards.
As Albion piled forward for an equaliser, Wigan almost doubled their lead in time added on but Lowe was denied in a one-on-one with Johnstone.