United is in 12th place and two points above the relegation zone. Longstaff clipped the crossbar in the first half and sealed a dream debut with the only goal in the 72nd minute. Jetro Willems ran at the static United defense and cut the ball back for Longstaff, who let fly from outside the penalty area past David De Gea in the United goal.
Longstaff started alongside older brother Sean as one of five changes Newcastle coach Steve Bruce made to the team which was beaten 5-0 at Leicester last weekend. United States defender DeAndre Yedlin started for Newcastle for the first time since April 6 after recovering from groin surgery.
United manager Solskjaer also made changes in a bid to kickstart his side's poor season, but it wasn't enough to prevent United's third league defeat in eight games. The 11th straight winless away match will inevitably increase the focus on Solskjaer and the structure above him.
Harry Maguire missed United's best chance with a header just wide from a corner before the break. Bruce enjoyed his first home win as Newcastle manager — and his first win as a coach over his former side United at the 23rd attempt across all competitions.
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