Romelu Lukaku scored his 100th Premier League goal as Manchester United strengthened their grip on second place and dented Swansea's survival hopes.
Lukaku gave United an early lead when he collected Alexis Sanchez's pass to fire in with the aid of a deflection.
Sanchez's crisp strike soon doubled the advantage – only his second league goal for United – as the hosts dominated.
Swansea improved after the break, Tammy Abraham twice denied by David de Gea, but United were always in control.
Jose Mourinho's side re-opened a two-point gap over third-placed Liverpool, who won 2-1 at Crystal Palace earlier on Saturday.
Swansea stay three points clear of the relegation zone but drop down a place to 15th.