so what is the earliest Nole can lose his no 1 rank ?
If Murray wins Miami, he'll be 3200 points behind.
Murray defends 270 points from MC and Barcelona, so he could improve by 1230 points there. Djokovic could lose his 600 from MC. That would leave Murray 1370 behind. Since Djokovic defends only 180 in Madrid, even a win there would be insufficient for Murray. So the earliest possibility is Rome.