They have won nine of the last 11 Premier League titles between them. They are England's last two Uefa Champions League winners.
United are not in the top four, Chelsea not in the top half. Achievers have become the season’s greatest underachievers.
Yet the defending champions are unbeaten in the calendar year. The most decorated club in Premier League history have five wins in seven games in 2016.
Such a run would have seemed normal for much of United’s recent past. After ending 2015 without a victory in eight, their worst sequence since 1990, it represents a turnaround.
Each can date the change of fortunes back to Chelsea’s visit to Old Trafford on December 28.
United showed positive intent and created chances, which was a welcome rarity. For once, they were forgiven for a goalless draw.
Chelsea showed their mettle. Weakened by injuries and lacking a specialist striker, they nonetheless averted a 10th defeat of the league season.
It offered a snapshot of the differing qualities each has provided in a recent renaissance.
Chelsea have prospered by being more solid, United by being more stylish.
Guus Hiddink favours a two-man defensive shield in the midfield. John Obi Mikel has been recalled and reinstated. Hiddink has cited the need for balance.
United hinted at a renewed interest in goals when they last faced Chelsea. They have since provided proof positive, scoring three times in each of the last two games. Again, that would not have been noteworthy for long swathes of time. After the barren streak of 15 matches, yielding only 12 goals, meaning that a google search of “Louis van Gaal” and “boring” produces 415,000 results, any excitement is overdue.
In keeping with the sense of confusion pervading at Old Trafford, there are contradictory explanations.
Both Wayne Rooney and Jesse Lingard have said that United’s players had now been given freedom to express themselves.
Yet, while discussing a change of policy, Van Gaal, in a different room, insisted they always had such licence.
Rooney’s argument is more persuasive. United are not merely passing the ball forwards. They are passing it faster.
Van Gaal, like his compatriot Hiddink, likes to talk of balance. He long complained he lacked it, insisting he wanted speedy wingers.
When he finally moved the slow, creative Juan Mata infield, he had pace on either flank. Rooney has seven goals in as many games, Anthony Martial three assists in two from the left flank.
Yet this represents a test if they have the boldness to attack away from home against what are, despite what the league table suggests, elite opponents.
It is an examination for Chelsea, too. They are yet to win a league game at home under Hiddink. With Manchester City and Paris Saint-Germain due at Stamford Bridge in the next five weeks, it serves as a dress rehearsal for games that figure on a potential path to silverware.
It should show what his preferred side is. If Eden Hazard, only a substitute in Wednesday’s stalemate with Watford, is recalled, does Oscar or Willian drop out?
Hazard’s last start against United came as a striker because, remarkably, Diego Costa is yet to face them. A combination of injury and suspension mean he has missed the last three meetings.
Chelsea’s resident wrecking ball has the capacity to upset smooth recoveries. The truth is Chelsea’s revival has been pockmarked with draws and United’s, apart from a fortunate win at Anfield, has consisted of games they would be expected to win.
Now a bullish Van Gaal believes a title challenge has been resumed. A Chelsea victory, however, would make this the first season in a quarter of a century when neither has been a contender to win the league. While one Dutch manager is on a damage-limitation exercise, he could cause untold harm to another.
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