If Anthony Martial had dared to dream about how his Manchester United debut would pan out he would probably have dismissed as idle fantasy any notion of scoring a wondergoal to down their fierce rivals Liverpool.

The footballing fates were certainly smiling on the French teenager as he danced past three flailing defenders and slotted the ball calmly into the back of the net, sending the home fans wild and prompting an ironic chorus of 'what a waste of money'.

The winger capped an excellent 3-1 victory with the moment of the match and announced his arrival to a fanbase who had been openly questioning the wisdom of spending an initial 36 million pounds ($55.54 million) on a player who had shown little more than potential at former club Monaco.

United manager Louis van Gaal, who had come under scrutiny for sanctioning the deadline-day deal this month and had even been accused of 'panic-buying', was suitably impressed if typically understated.

"Not a bad goal I think," he told Sky Sports. "He did alright. He scored a marvellous goal and physically he can play in the Premier League."

Van Gaal had oddly been more impressed with United's drab first-half performance, when they dominated possession but created nothing, than their thrilling second-half display.

A goalless first half was followed by a much more determined start to the second when Daley Blind beautifully curled United into the lead from a training ground-inspired set piece and Ander Herrera doubled the advantage from the penalty spot.

Christian Benteke's spectacular late bicycle kick gave Liverpool faint hope their tame performance did not truly merit before the 19-year-old Martial, who had come on as a 65th-minute substitute, ended the contest with four minutes remaining.

While the end-to-end conclusion had fans on their feet, it clearly was not to Van Gaal's liking.

"We played better in the first half," the Dutchman said. "We had far more control but we didn't create much.

"I am very happy with the first goal because that is what we practised in many training sessions and now it is coming out.

"The first goal decided the match because they had to come at us, giving us more space so we could score more."