Liverpool ultimately cruised to their win as substitute Mohamed Salah scored a fifth in stoppage time, coolly converting a close-range shot in off the crossbar for his ninth goal of the season.
Alexis Sanchez, who was closeto joining Manchester City on transfer deadline day, started the day on the bench, but came on for Welbeck with 15 minutes remaining.
And after going close twice, Anthony Martial ended his 491-minute goal drought by collecting Paul Pogba's pass and beating Ramsdale at the second attempt.
In windy conditions, the champions took only six minutes to make the breakthrough when Arda Turan fired home a close-range finish from Jordi Alba's low cross.
Manchester City beat Manchester United 2-1 to extend their perfect start to the Premier League season and end that of their local rivals in an entertaining and action-packed encounter at Old Trafford.