The Brazil playmaker headlined a devastating display by Liverpool in its 7-0 thrashing of Spartak Moscow at Anfield on Wednesday, with the other three members of the attacking "Fab 4" - Roberto Firmino, Sadio Mane and Mohamed Salah - also scoring.
A Liverpool win would not only see them through as winners of the group, but it would also be the first time any single country has sent five teams through to the knockout stages.
15 minutes into the game, Coutinho doubled the lead after a lovely play between Sadio Mane, Salah and Roberto Firmino.
Spartak's defence had been scrambled from the outset and they were punished for a fifth time in the 50th minute, Coutinho finding space in the area to wrong-foot Selikhov with a deflected effort off Salvatore Bocchetti.
Liverpool's obliteration of the Russian side saw them amass a tally of 23 goals this group stage campaign, the most ever recorded by an English team in the Champions League.
Liverpool was one of four English teams to top a group, along with Manchester City, Manchester United and Tottenham. Having only drawn with this opposition on the opening match-day, they went into this big game hoping to turn the tables on home soil and ensure their fans were enjoying football at Europe's top table come 2018.
Liverpool's early onslaught began from the spot, Coutinho coolly sending the goalkeeper the wrong way after Salah had been dragged down by Giorgi Jikia. It was a similar story in 2005 when Everton finished above them to claim the league's final Champions League qualification spot, only for the Reds to throw a spanner in their local rivals' works by winning the competition outright.
Coutinho added another two minutes later, latching onto another Milner cross and firing another left-footed effort in via a Spartak defender to make the score an astounding 5-0 by the 50th minute.
They are already on course to better the 110 goals scored when Brendan Rodgers took to Liverpool to within a whisker of the Premier League title in 2013-14.
"We opened the game perfectly and after we took the lead we didn't have to defend". Spartak, who needed a win to progress, drop into the Europa League.