The teams are separated by two points as they fight to be runners-up to champions-elect Manchester City. Both teams are currently involved in this seasons Champions League as well, with Liverpool (17-9-3) reaching the round of eight for the first time since 2009 and United (19-5-5) attempting to join them next week after holding Spanish side Sevilla to a 0-0 draw on the road a fortnight ago.
Liverpool advanced after a scoreless second-leg draw Tuesday against FC Porto, a match that was essentially a dead rubber after the Reds ran riot in the first leg in Portugal, scoring five goals without reply. On Tuesday, Sadio Mane hit the woodwork while Porto goalkeeper Iker Casillas did well to keep Liverpool off the scoresheet with saves on both Danny Ings and Roberto Firmino.
"It was a big challenge for us, to be honest, in the preparation, it was different to other games, of course," Liverpool manager Jurgen Klopp explained. "I think the boys did really well - we showed a fantastic attitude, a few pieces of really nice football and we defended very serious. Now we are in the next round, so I don't need any more positives."
The first-leg victory allowed Klopp to make five changes from the side that defeated Newcastle United 2-0 last weekend, resting starting central defender Virgil Van Dijk and allowing leading scorer Mohamed Salah to stay fresh by playing just the final quarter-hour.
Liverpool are unbeaten in their last seven matches (5-2-0) in all competitions and have conceded just once in their last five.
"It was an aim for us, to build on the recent form of not conceding any goals and having a lot of clean sheets," keeper Loris Karius said after posting his 10th clean sheet in 19 matches. "The boys are doing well. It doesn't matter who comes in, they do the job. That's always a good thing for me and for the whole team."
United are unbeaten in their last four in all competitions and rallied for their second straight league victory Monday, beating Crystal Palace 3-2 at Selhurst Park. Chris Smalling started the fight back from two down just before the hour mark and Romelu Lukaku drew them level in the 76th minute before Nemanja Matic unleashed a screamer of a right-footed shot from outside the penalty are in the first minute of stoppage time for the winner.
"I cannot tell you half of the things I told my team at half-time because there would be lots of bleeping on television," United boss Jose Mourinho told MUTV. "But what I can say was all about the tactical positioning. To come back from 2-0 down away from home against a team that is desperate for points, it gives us a great feeling."
Mourinho's introduction of Marcus Rashford at halftime was influential, and Juan Mata added the pressure through the midfield when he entered in the 67th minute. It was just the second time United conceded two goals in a match this season and won, with the other their 4-2 victory at Watford on Nov. 28.
"I think it was a case where it was a never-say-die attitude and the character of the guys to win the game after going 2-0 down," Smalling said. "We dug in and it was a big win in the end. It probably knocks some of our competitors who were probably enjoying it when we were losing 2-0. … We knew we had to be on our toes and it was a good battle - I enjoyed it."
Lukaku has four goals in his last four matches, giving him a team-best 22 in all competitions, and United supporters are hoping his marker against Chelsea - his first in seven matches against teams in the top six of the table - is a sign of things to come against the Premier League's best.
"It is a big game against Liverpool," said Mourinho, who did not hold the same opinion ahead of the reverse fixture at Anfield that ended in a 0-0 draw. "I think we both want to finish in the top four, but we both want to finish second so, yes, it is a big game. Then we have Sevilla in the Champions League knockout and Brighton in the FA Cup knockout, so three big matches at OId Trafford."
The long-time rivals are renewing acquaintances for the 200th time, with Manchester United claiming 79 wins to Liverpool's 65. The teams have played to level terms in the other 55 meetings.
United had just one shot on target at Anfield in what was mainly a dour affair that also served as the fourth consecutive stalemate between the sides. Liverpool has the last win in this rivalry, a 2-0 triumph at Anfield in the first leg of the 2016 Europa League round of 16.
The Red Devils, though, are 2-2-0 in their last four at The Theatre of Dreams against Liverpool and 8-2-1 in the last 11, with the only loss a 3-0 setback in the 2013-14 season. Last season's corresponding fixture was a 1-1 draw as Zlatan Ibrhaimovic's goal six minutes from time canceled out a penalty by James Milner on 27 minutes.