They might both be below Manchester City in the Premier League, but the battle between Manchester United and Chelsea has become one of the most interesting of the season.
And it is nothing to do what what's happening on the pitch.
The ongoing war of words between Jose Mourinho and Antonio Conte continued after Chelsea's goalless draw at Norwich in the FA Cup on Saturday, after which Conte branded Mourinho "fake" and "a little man."
In his own Chelsea days, the Manchester United boss picked fights with the likes of Arsene Wenger and Rafael Benitez as he sought to do anything he could to gain an advantage for the Blues, but now he's in the red corner it is predecessor Conte who is lined up in his crosshairs.
The pair went head-to-head on occasion last season - Mourinho's first at United and Conte's first in England - but since the summer things have got a lot more heated.
Here are just five reasons why.
1. Menace in the market
Ask anyone where Romelu Lukaku was going at the beginning of the summer and the answer would have been simple. Chelsea.
It had been the accepted state of affairs that the former Blues forward was going back to his former club and not joining up with his former manager at Old Trafford, only for Manchester United to dramatically swoop in and buy Paul Pogba a new mate to play with.
Similarly, United attempted to muscle in on the deal for French midfielder Tiemoue Bakayoko before he went to Chelsea.
And there was also an impasse between the pair ove Nemanja Matic,who eventually made an awkward switch to Old Trafford.
2. Last season's flashpoints
Chelsea and United went head-to-head three times last season, and Mourinho and Conte bashed heads almost as often.
The pair were seen going at each other in both the league clash at Stamford Bridge and March's FA Cup meeting in west London, with Mourinho claiming that Conte showed him "a lack of respect" when his Blues side were 4-0 up in October's league meeting.
Presumably he'd have been fine with 3-0.
3. Mourinho's desire to stop Conte in his tracks
Like Mourinho, Conte won the Premier League title in his first season at Stamford Bridge. But Mourinho won it in his second too.
The Portuguese is fiercely proud of his Stamford Bridge legacy, holding three fingers up during last season's FA Cup defeat at denote the amount of league titles he'd won at the club.
He would have been desperate to stop the Italian from making it two out of two this season, and although that isn't going to happen because of Manchester City, the fact that his United side are also so far behind them would have tapped into Mourinho's psyche.
4. Conte's bid to do what Mourinho never did
But for all that Mourinho achieved at Chelsea, he never won the Champions League with the club, something that Conte will have a chance to do for the first time in 2017/18.
Manchester United will be in the competition too, of course, but that will only strengthen Conte's desire to outdo Mourinho when it comes to Chelsea's European history, and if the pair were to meet in Europe then sparks could fly.
5. Revenge
It could be said that both bosses suffered their worst performances of last season against the other, with Mourinho's United losing 4-0 against Chelsea in October and then Conte's Chelsea turning in a strangely lethargic performance in losing 2-0 to Mourinho's United in April.
Although the league was pretty much won at that stage, Conte will have seen plenty to worry about in that game - including a Mourinho masterclass in how to nullify Eden Hazard - and so getting one over his rival will be crucial when they meet.