London - Manchester United manager Jose Mourinho has an opportunity to score a seismic victory over his old foe Pep Guardiola when his side visit misfiring Manchester City on Thursday.
Guardiola oversaw a one-sided 2-1 win when he and Mourinho resumed hostilities in September - each at the helm of a new club - and was generally felt to have made a bigger impact than the Portuguese in the season's early months.
But having been condemned to a trophy-free first season at City by Sunday's FA Cup semi-final loss to Arsenal, Guardiola will lose his hold on a top-four place if United prevail at the Etihad Stadium.
"It is going to be the game of the season," predicted United's Spanish midfielder Ander Herrera.
"We are one point behind them. If we win we have the chance to finish in the top four. If they win, it is going to be very difficult.
"Is it make-or-break? Probably. Both teams are in a good moment so if one of us wins the game we are not going to lose a lot of games or make mistakes after that. Us or them. It is going to be key."
Mourinho, Guardiola's bete noire during their time in Spain, has played down Herrera's remarks, telling Sky Sports: "He says that because I always say that about the next match."
But the United manager will know that victory would give United the edge over City in the quest for Champions League qualification.
United have struggled for fluency this season, drawing no fewer than 12 games, and spent four months grimly locked in sixth place in the table.
As the days grow longer, however, the prospects of a successful end to the season appear to be getting brighter.
United have already won the League Cup, face Celta Vigo in the semi-finals of the Europa League and showed in their stunning 2-0 ambush of league leaders Chelsea that they are a match for anyone.
Avoid defeat on Thursday and they will equal the club's record for the longest unbeaten run in a top-flight season -- a 24-game sequence enjoyed in 2010-11 by a United team who finished as champions.
Fatigue aside, the only other dark cloud on United's horizon is injuries.
Marcos Rojo and top scorer Zlatan Ibrahimovic have both been ruled out for the rest of the season with knee ligament damage, while Paul Pogba was forced off during Sunday's 2-0 win at Burnley.
Despite Mourinho's entreaties for them to play through the pain barrier, centre-backs Chris Smalling and Phil Jones are both expected to miss out again, along with Juan Mata.
Mata scored the winner when the teams met in the League Cup fourth round in October.
Ibrahimovic's injury, meanwhile, has opened the door for Marcus Rashford, who netted the game's only goal when United last visited the Etihad in March 2016.
Anthony Martial will hope to start after scoring one goal and making the other for Wayne Rooney at Burnley.
Guardiola is praying key duo David Silva and Sergio Aguero will be fit after both were substituted during the 2-1 loss to Arsenal at Wembley due to a hamstring injury and a dead leg respectively.
John Stones, Bacary Sagna and Fernandinho are also injury doubts, while it is not clear what role - if any - Gabriel Jesus might be able to play following his return from a broken foot.
Securing a top-four finish is Guardiola's last chance of salvaging something from his first season in England and midfielder Yaya Toure knows his side face a battle.
"It is going to be difficult. It is very tight," said the Ivorian.
"United are doing well, Arsenal are going to have confidence and Liverpool lost (against Crystal Palace), but it is not finished yet. This league is going to be very tough.
"It is a very big game, an important game. We have to do the job and we will see what can happen."