1. Points accumulated in the 'mini-league' of the top five teams are becoming ever more crucial in deciding the championship. Chelsea have usually lagged behind Arsenal and Manchester United in this respect, but this season they are leading the way with 17 points out of a possible 21 (and only two goals conceded). Arsenal have a paltry five points. 2. Chelsea have struggled in London derbies - until this season. They have taken 21 points out of a possible 27 and, most importantly, have matched Arsenal, drawing both their league clashes. Their 2-2 draw at Highbury in December, twice coming from behind, was a psychological watershed. 3. Christmas has always been a time for giving rather than receiving for Chelsea, but they took a maximum 12 points over the festive season this time, despite some tough fixtures. They approached Christmas with a five-point lead and 10 days later, after four straight wins, had stretched that advantage to seven points. For Jose Mourinho, whose father was once sacked from a manager's job on Christmas Day, it was a personal triumph. 4. Last season their defence was almost as good as Arsenal's but they were let down by an inconsistent attack, especially at home where they failed to score in four of their last 10 league games under Claudio Ranieri. Mourinho's switch to 4-3-3 has made a difference, with Chelsea suffering just three shutouts in 18 home league games (crucially, they haven't lost any of those games).