Liverpool were given a glorious glimpse of a bright future on a historic on Sunday at Anfield as Manchester United were ruthlessly crushed 7-0 to match their heaviest ever competitive defeat.Roberto Firmino came off the bench to inflict the final wound on a beleaguered United, who had lost just once in their previous 22 games.But in the week it was reported the Brazilian will leave Liverpool at the end of the season, the Reds' new-look front three finally clicked as Cody Gakpo, Darwin Nunez and Mohamed Salah all scored twice.READ | Man United coach slams 'unprofessional, unacceptable' players after Liverpool humiliationThe triumvirate of Salah, Firmino and the now departed Sadio Mane took Liverpool back to the top of English and European football under coach Jurgen Klopp.In a desperately disappointing season with Liverpool still sitting only fifth in the Premier League, the signings of Nunez and Gakpo for a combined £100 million have been questioned.But both enjoyed by a distance the best day of their Liverpool careers to prove the doubters wrong."We showed tonight what we could be, what we can be and what we have to be from now on," said Klopp. "We don't talk about the scoreline, we just talk about the performance."The fact that both players were once linked with United will sting even more for the Red Devils with a centre-forward a priority this summer if the progress they have made under Erik ten Hag is not to stall next season.Gakpo was seen as an obvious target given Ten Hag has not been slow to shop in his homeland with the signings of Antony, Lisandro Martinez and Tyrell Malacia.But Liverpool are beginning to reap the rewards of jumping ahead of the competition to sign the Dutch forward from PSV Eindhoven in