Manchester United ought to have been aware of Xherdan Shaqiri's potential to decide football matches.
On his Liverpool debut in pre-season, the Swiss playmaker announced himself with a marvellous bicycle kick in a 4-1 victory over Jose Mourinho's team in Ann Arbor.
In retrospect, it was clear from that evening in the United States that these were two teams heading firmly in opposing directions. The possession stats - 65 per cent to Liverpool, 35 per cent to United - were identical to Sunday's procession at Anfield and Shaqiri had a pivotal influence in both matches.
Shaqiri did not hang about on this occasion. He arrived on the pitch in the 70th minute, scored one by the 73rd minute and put Liverpool out of sight in the 80th minute.
He has now scored five goals - more than Alexis Sanchez has managed at Manchester United since joining in January.
Shaqiri was something of a surprise purchase by Jurgen Klopp in the summer. At £13m, Liverpool activated his release clause upon relegation at Stoke but this is not a player who comes with guarantees.
Shaqiri had operated at major clubs before, failing to nail down a place at Bayern Munich or Inter Milan under Pep Guardiola and Roberto Mancini.
In Germany, some questioned whether he had the tactical intelligence for the highest level.
Shaqiri, too, has always given the impression of craving protagonist status. At Liverpool, he must be subordinate to the prime front three of Mohamed Salah, Roberto Firmino and Sadio Mane.
During Liverpool's first five Premier League games of the season, Shaqiri played only 27 minutes.
Some might have wondered if he would have the requisite patience or if he would mope around and feel sorry for himself.
Instead, Shaqiri has embraced his part as the fourth man and his form has been such that he now offers Jurgen Klopp variety and the possibility to play with his preferred 4-3-3 or with a 4-2-3-1 where Shaqiri floats amid the usual trio.
It has not been perfect. On his debut against Southampton, Shaqiri scored one and made one as Liverpool raced into a 3-0 half-time lead - but he was then substituted at the break as Klopp wanted more tactically.
Four days later in the Carabao Cup defeat by Chelsea, Klopp ran onto the pitch at the full-time whistle and publicly admonished Shaqiri for failing to take a set-piece in the closing moments. During the game, he had repeatedly urged his new signing to press harder.
At Stoke, the accusations of lethargy, particularly during their relegation battle last season, began to amplify.
Charlie Adam recalled: 'We needed everyone to run, scrap, fight, dig, kick - do whatever it takes to stay up, but we fell short. We knew he was a match-winner, he was, but we felt we should have had more respect from that point of view.'
Yet a motivated Shaqiri is a player of the highest quality. Sportsmail columnist Peter Crouch remembers his first training session with the club.
Crouch said: 'Shaq, as we got to know him, scored a hat-trick in a five-a-side game.
'You might think there is nothing unusual about that but when I tell you one of his goals involved him chipping the goalkeeper from about eight yards, you will appreciate why this stayed in my mind.'
Thankfully for Liverpool, this is the Shaqiri decorating and defining their performances.
When Shaqiri moved into his home in the Cheshire suburbs after joining Stoke, one of his neighbours handed him an old Manchester United programme adorned by the face of his new manager Mark Hughes.
After Sunday at Anfield, Shaqiri has a new matchday programme to treasure.