Drogba dilemma for title showdown
Champions United have a one-point advantage over their nearest rivals and, with Chelsea facing two more tough away assignments at Liverpool and Tottenham Hotspur this season, the onus is on the Londoners to go for broke at Old Trafford.
Ancelotti has favoured a 4-4-2 system, featuring a diamond shape in midfield, for much of the campaign but a switch to 4-3-3 since last month's Champions League defeat by Inter Milan has led to an avalanche of 12 goals in two games.
The tactics deployed in last week's 5-0 rout of Portsmouth and 7-1 thumping of Aston Villa were a throwback to the formation used by former coach Jose Mourinho for Chelsea's Premier League title triumphs in 2005 and 2006.
The recent switch to 4-3-3 meant the Londoners could again play to their traditional strengths, with one centre forward (Drogba or Nicolas Anelka) flanked by two wingers.
It is a system that seems to find favour with Chelsea captain John Terry.
"The formation suits us probably a little bit better with the two wide men," Terry told the club's in-house television station.
"Over the years we have had a lot of success with that. We stretch teams."
The simple truth is that Chelsea's results this season are stunning with Anelka at centre forward.
In the 10 games Drogba has missed and Anelka has led the line, Ancelotti's men have a 100 percent winning record with a tally of 33 goals scored and only five conceded.
Chelsea appear less fluid when Drogba plays, not because of any lack of thrust from the Ivorian but because if he and Anelka play together it invariably means the Frenchman occupies a wide role in which he is less comfortable.
In that position Anelka is unable to offer the same direct running and dribbling style as Florent Malouda, Joe Cole, Salomon Kalou or Daniel Sturridge, who are also more adept at filling wide defensive slots when Chelsea lose possession.
Many pundits thought the Londoners would struggle when Drogba was away on African Nations Cup duty in January.
However, the opposite was true as Anelka switched into the centre and Chelsea won all five games without Drogba, the team amassing 19 goals and conceding just three.
Drogba was rested again last Saturday and Anelka led the attack in style for the 7-1 drubbing of seventh-placed Villa.
Drogba has always linked well with Frank Lampard but it appears the England midfielder roams into even more dangerous positions when Anelka plays centrally.
Lampard hit five goals in Chelsea's purple patch in January and bagged four, including two penalties, against Villa.
"The build-up was fantastic to all the goals, the penalties as well," said Lampard after taking his tally to 151, the club's th