Chelsea and Manchester United meet on Sunday in a Premier League grudge match which could impact both sides' title bids.
United currently sit second in the table, five points behind Manchester City. Chelsea, meanwhile, are four points behind United in fourth.
Here, we look at the talking points ahead of the Stamford Bridge contest.
1. MOURINHO MOTIVATION
Humiliated in a 4-0 loss on his return to Stamford Bridge last season, Jose Mourinho was next called "Judas" by a section of Chelsea fans during March's 1-0 FA Cup loss. He responded by reminding them of his achievements at Chelsea.
No longer The Beloved One, Mourinho would relish adding to Antonio Conte's problems with a victory which would keep United close to Manchester City at the top of the table. The question is how will he do it? By his tried and tested method of parking the bus? Or by playing the 'United way'? Former Blues Nemanja Matic, Romelu Lukaku and, likely to a lesser extent, Juan Mata could also have an impact for the visitors.
2. HISTORY REPEATING ITSELF?
Chelsea are already nine points behind leaders Manchester City entering this weekend's Premier League fixtures. Should Mourinho's men win, then the Blues' chances of retaining the title won in Conte's first campaign will look ever more unlikely.
It is a situation reminiscent of two seasons ago when Mourinho's title-winning Blues imploded. Then Chelsea lost nine of their first 16 Premier League matches and Conte's Blues have been beaten in three of their first 10. There has been regular speculation over the Italian's position being precarious - and if Mourinho's latest return sees United take home three points, things could unravel very quickly.
3. STRIKING FORWARDS
When it became apparent Diego Costa - a Mourinho signing - had no future at Chelsea, it was widely assumed Lukaku would return to Stamford Bridge. Instead the Belgium striker swapped Everton for Manchester United, and Chelsea pulled off a perceived coup in signing Alvaro Morata from Real Madrid.
Lukaku scored seven in seven Premier League games and Morata six in six. But both are without a goal in six games in all competitions. Both men will be keen to rediscover their scoring form against top-level opposition.
4. MIDFIELD SUPREMACY
Chelsea will be desperate for N'Golo Kante to be fit following a hamstring injury which has seen him miss six matches. Kante's athleticism and intelligence are key to the balance of the Blues. Mourinho has hailed the signing of Matic from Chelsea.
The strengthening of a title rival left some pundits scratching their heads, while Conte was displeased at Matic's departure. But the Serbia midfielder's contract was running down and Chelsea took the best financial offer. It will be intriguing to see Matic against his replacement, Tiemoue Bakayoko. Injuries have troubled Chelsea, but United are without midfielders Paul Pogba, Michael Carrick and Marouane Fellani.
5. PHONEY WAR?
Manchester City's performances and results have made them title favourites. Some reckon this is a must-win game for United as well as Chelsea due to the form of Pep Guardiola's league leaders. It is difficult to disagree.
This may be a grudge contest, but it is by winning consistently and in matches with City (Chelsea have already lost 1-0 to City this season) that Chelsea and United can join the title race. The destination of the trophy will not be decided at Stamford Bridge on Sunday.