Saturday’s game at Bramall Lane was a scrappy affair during which both sides struggled to create clear-cut chances.
But Wijnaldum’s well-struck 70th-minute volley, which squirmed under United goalkeeper Dean Henderson, made it seven victories from seven top-flight outings this term for the Reds.
Team news
Liverpool were unchanged from their previous Premier League outing, last Sunday’s 2-1 victory at Chelsea.
Divock Origi returned to the bench after recovering from an ankle injury.
First half
A possession percentage of 87.5 with 10 minutes gone told the story of the Reds’ early domination of the ball and territory.