Look at Man United, do you see anything to smile about?

Manchester United manager Erik ten Hag. [AFP]

Erik ten Hag is already back under extreme pressure at Manchester United after flunking his first big test since the club decided to keep faith with their Dutch manager.

United's chastening 3-0 home defeat at the hands of Liverpool on Sunday left them languishing 14th in the Premier League table just three games into the season.

Co-owner Jim Ratcliffe, seated alongside the new Old Trafford hierarchy, had his head in his hands as United showed all their old failings against their bitter rivals.

Ten Hag's side went toe to toe with Arne Slot's men for the first half an hour but costly errors from Casemiro and clinical finishing from Luis Diaz put the visitors in total command at half-time.

Mohamed Salah scored his customary goal against United in the 56th minute and Liverpool saw out the game with relative ease in a rapidly emptying stadium.

For long-suffering United fans, it appears to be a case of rinse and repeat.

The club, who have not won the Premier League since Alex Ferguson's final season in charge in 2013, appear to be stuck in a seemingly endless cycle of mediocrity despite multiple changes of personnel on and off the pitch.

Ten Hag was handed a contract extension in July, but only after United had considered alternatives following a season in which they finished a lowly eighth in the Premier League.

United's 2-1 victory against Manchester City in the FA Cup final in May proved vital after it seemed likely the Dutchman would be sacked.

The embattled Ten Hag was forced to defend himself after Sunday's defeat, which followed a last-gasp win against Fulham and a defeat at Brighton.

"It is just the third game in the season, we have to build a new team," said the 54-year-old. "I explained this so many times, we will build this new team, we have young players and players to build in."

The former Ajax boss can point to mitigating circumstances -- Manuel Ugarte, United's new midfield recruit from Paris Saint-Germain, was not available while another recent arrival, defender Leny Yoro, is injured along with Mason Mount, Luke Shaw and Rasmus Hojlund.

Former Real Madrid midfielder Casemiro was at fault for both of Diaz's goals and was hauled off at half-time while forward Marcus Rashford looked desperately short of form and confidence.

Whether or not United now regret their decision to stick with Ten Hag, former Manchester United captain Gary Neville, a Sky Sports pundit, believes he will be given until Christmas to turn things around.